In particular, I'm trying to figure out feats and possibly a multiclass dip as I plan my build out ahead of time.

We've played one session, but I'm allowed to rebuild most things.  (Can't change my species, but that's pretty much it).

Character Concept: Stealthy caster who specializes in spells that don't break hiding.  Illusionist will make it so none of my illusions will require verbal components once i hit level 3, and I grabbed spells like Catapult and Snare (the latter of which can also be 'delivered' to the target area by the familiar, since it's a touch spell...)  Wood Elf will pick up Pass Without Trace to help make the party stealthy.  I took the criminal background for stealth, sleight of hand, and thieves tools proficiency.  

Attributes currently 8 16 10 17 8 14  (Starting from the 15 15 14 10 8 8 array)

Dilemma(s):

1. I want to get Deception and expertise in at least Stealth.  I could do this with the Expertise feat, but this feels inefficient.

-- Is it worth a 1 level dip into Rogue?  I could custom the background to give me, idk, disguise kit proficiency or something instead.  Get Thieves Cant, 2 expertise, and 1 extra skill.   Saves me the need to take the Expertise feat.  I also get light armor and a sneak attack die, not that I intend to be making attack rolls.

-- Starting Rogue would lose me access to Knowledge Arcana and give me dex instead of wis for save proficiency (which given my wis is bad and my dex good, probably a net worse trade), even if it does give me an extra skill and finesse weapon proficiencies.

2. OTOH, I really don't know what I want to do with my feats. 

-- Considered Shadow-Touched, which plays into my background well,  but the one session dropped a scroll of invisibility in my lap already, I'm already taking all the interesting first level illusion spells anyway, and 1st level necromancy spells aren't appealing.

-- Since I'll get minor image as a bonus action at Wizard 3, Telekinetic doesn't feel as good as it could be, because I'll generally have good uses for my bonus action.

-- I'm not sure how good Observant or Keen Mind are.  I can already get expertise in Investigation via Wizard 2's Scholar, so Keen Mind would probably be Knowledge Arcana expertise.  How good is study as a bonus action?  Observant would get me expertise in Perception and search as a bonus action, so seems the more worthwhile of the two.  (Considering I'm starting at -1 before proficiency bonus, expertise would really help).

--There's an organizational progression system, which includes sources of advantage on stealth checks eventually (since I chose the criminal organization), and that devalues Skulker quite a bit (otherwise it would be a priority).

--War Caster is not amazing for the concept, but if i do find myself hidden next to an enemy that moves away, casting something like Phantasmal Force or Phantasmal Killer as a Reaction sounds like fun.  Not sure it's worth a feat, though.

So I'm looking at one of:

--Expertise, Observant, Keen Mind, +2 Dex  (Swap Expertise for... idk, telekinetic just for verbal-free mage hand? if I'm doing the rogue dip)

--Choose one feat, +2 Int, +2 Dex, +2 Dex (ends 20 in each)

--Something where I take metamagic adept (Heighten and Subtle) for a little more versatility in casting while hidden or forcing a fail against a critical spell? (Probably replacing one of the +2 Dex in the second option above).

So: (1) Thoughts on feat choices? (2) 1 level of Rogue worth giving up spellcasting progression? (3) Is Alert worth it?  It wasn't super useful in the one adventure played so far.  Should I be looking to have a different starting feat?

I dont have much experience with illusion wizard but I can try to help a bit. So for your feats i always like fey touched over shadow touched but both are A tier feats. I find metamagic adept is most useful on a sorcerer and it is just a little annoying on anything else(exception for warlocks because quickened spell EB is great even two times a day). Alert is a decent feat and particularly useful On a wizard so you can put down a key spell first. Keen mind and observant are in my opinion nothing special but my campaigns i play in tend to be more combat than the other two pillars so YMMV. Wizard is almost always better going straight wizard as levels in another class just delay spell slots and spell level. That being said though if you are playing 2024 rule set then the 18th level feature is no longer a must(I think) as all the spells must be an action but in 2014 you always take it for shield and other fun reaction spells

Thats basically all I’ve got for now so happy adventuring!

In particular, I'm trying to figure out feats and possibly a multiclass dip as I plan my build out ahead of time.

Build him out has a single class the best you can.  Any MC dip can lead to falling behind, so you need to to determine your actual weaknesses as a pure Mage.   Once you determine those weaknesses, then look at Rouge/?? to fill that weakness.   The basic choice is a loss of higher spells vice filling that weakness.  Look at 3rd level and a 5th level character.  

Realize that your illusionist subclass if you dip will not show up until you are a 4th level.  Chances are those great spells that show up for a 5th level mage are delayed until 6th level.  Is that delay worth it?

Taking a dip in levels when you start as a high level character is not bad.  But starting at level 1 can be painful as every session you can 2nd guess yourself as you experience that delay pain.

Stealth is a major factor for your build, but should it be?  As an illusionist, you can do so much to confuse the opponents do you actually need to be stealthy?  Do you really need to be in a position/location that requires you to be stealthy?   Isn't stealth more about getting into position then actually staying and hiding?  V/S are major impediments to being hidden.  Any movement/noise can give away a position.  If you can eliminate V/S, then it is easy to hide.  And lack of S can be achieved via warcaster feat with hands full, so how would the DM interpret that?

Criminal background is a great way to boost INT and get stealth.

As to Alert.  Like my questions on how bad do you need stealth, do you need to be one of the 1st people to go in a round?  If you don't then Alert might not be a top choice.

Shadow touch - is there a Level 1 spell you really need?  If not, is invisibility once a day worth while?

Keen mind "study action" basically gives you a skill check roll during your BA to tell everyone you party how to fight X.  That will show your position as the answer you find out needs to be communicated to the party.

As mentioned Warcaster can allow S to occur if your hands are filled.  Very good for a melee fighting mage, as for you, you need to discuss this with the DM as to the assistance it can provide.  But your desire to be stealthy, results in probably never getting an opportunity attack.

Normally, creating a good illusionist is very difficult in 2024, compared to my memory of much older illusionist classes, it has been severely nerfed, but if stealth is so important, I personally feel this is even more difficult to create a great illusionist.

Quote from Character77006 >>

In particular, I'm trying to figure out feats and possibly a multiclass dip as I plan my build out ahead of time.

 

Build him out has a single class the best you can.  Any MC dip can lead to falling behind, so you need to to determine your actual weaknesses as a pure Mage.   Once you determine those weaknesses, then look at Rouge/?? to fill that weakness.   The basic choice is a loss of higher spells vice filling that weakness.  Look at 3rd level and a 5th level character.  

Realize that your illusionist subclass if you dip will not show up until you are a 4th level.  Chances are those great spells that show up for a 5th level mage are delayed until 6th level.  Is that delay worth it?

Taking a dip in levels when you start as a high level character is not bad.  But starting at level 1 can be painful as every session you can 2nd guess yourself as you experience that delay pain.

Stealth is a major factor for your build, but should it be?  As an illusionist, you can do so much to confuse the opponents do you actually need to be stealthy?  Do you really need to be in a position/location that requires you to be stealthy?   Isn't stealth more about getting into position then actually staying and hiding?  V/S are major impediments to being hidden.  Any movement/noise can give away a position.  If you can eliminate V/S, then it is easy to hide.  And lack of S can be achieved via warcaster feat with hands full, so how would the DM interpret that?

Criminal background is a great way to boost INT and get stealth.

As to Alert.  Like my questions on how bad do you need stealth, do you need to be one of the 1st people to go in a round?  If you don't then Alert might not be a top choice.

Shadow touch - is there a Level 1 spell you really need?  If not, is invisibility once a day worth while?

Keen mind "study action" basically gives you a skill check roll during your BA to tell everyone you party how to fight X.  That will show your position as the answer you find out needs to be communicated to the party.

As mentioned Warcaster can allow S to occur if your hands are filled.  Very good for a melee fighting mage, as for you, you need to discuss this with the DM as to the assistance it can provide.  But your desire to be stealthy, results in probably never getting an opportunity attack.

Normally, creating a good illusionist is very difficult in 2024, compared to my memory of much older illusionist classes, it has been severely nerfed, but if stealth is so important, I personally feel this is even more difficult to create a great illusionist.

Casting with an S component does not break hidden from the hide action, only casting with a verbal component does.  So staying hidden with S components is RAW.  (Moving quietly is already covered by the stealth roll of the hide action, and there's nothing about somatic components which makes them noisy, or the hide action would mention them).  

There's no reason you couldn't be hidden and 5' from an enemy, but I agree that it would likely require too much work to set up frequently.

Combining minor illusion with a silent or major image while you are unseen allows for a lot of shenanigans, especially if I also have an unseen servant running about and/or am throwing objects around with catapult.  Or dropping a Phantasmal Force.  These give options for bluffing past encounters or creating havoc before combat even starts.  

And yes, casting from hidden is the basis of the character concept, so i absolutely need that.

As to tradeoffs, one level behind is annoying, but it's not 3rd level spells that are terribly interesting for Illusionists. (I'd probably take the Rogue dip at 4th level or 5th level, so not delaying 2nd level spells or illusionist subclass's 3rd level ability).  Between casting all my illusions silently, Minor Illusion, Catapult, Nathair's Mischief, Phantasmal Force, Rime's, and Colorspray, that's a pretty decent suite of combat options.  (Plus stealth allows for setting ambushes, where Snare and even something like Shape Water or Mold Earth can shine.)  And I'm picking up Pass Without Trace at 5th level regardless (species).  (Major Image doesn't really become interesting until 4th level slots, when it doesn't require concentration.  I'll admit Hypnotic Pattern is fun).

On the other hand, expertise in stealth is super important for routinely hiding (need to pass a DC15 to even be hidden in 2024).  And costing a feat is expensive, too.

And communicating with the party just requires the message cantrip.  (SM, whisper the message = doesn't break hidden).  Or ultimately Rary's will do it (which you better believe is high on my priority list for 5th level spells).

Anyway, the concept is stealthy AND illusionist.  So let's optimize in that box, rather than question the existence of that box.

I had difficulty doing an illusionist, and failed miserably making them stealthy, so good luck.