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!