I am working on a monk rogue (using above subtypes). Looking for help with level progression and feats/stat boosts

Is a  weapon die of 1D8 (2D8 with 1 KI point) and Sneak die 4D6 a good mix?  (MONK 12 / Rogue 8)

What level are you starting at, or is this more a theorycraft for future reference?  Stat order will probably be DEX then WIS as your top two stats after that it is up to you to determine if you want your investigative abilities to be stronger (Int Wis) which is part of the Inquisitive toolkit or increase survivability and get CON up. 

For one thing you will have an overlap of Evasion from both classes, I don't know if there is a great reason to go anywhere above 6th level for the rogue side of things, Uncanny Dodge and Expertise are handy.  Decide if you plan to have another couple strong skills and whether the expertise is worth it to you.  I think I personally would only go to level 5 with the rogue, and leave all the rest for monk.  This would result in a larger pool of ki at late game (if you get there) and you will still have some strong utility abilities from your rogue side. 

If you have any other ideas so far let us know maybe it can help us with your very broad question you asked.  

This is for a potential AL character.

Level wise, is higher Weapon die better than higher Sneak Attack?

ddb.ac/characters/18551769/dG01rW

I am wondering what is better.  I high Damage die for monk weapon (Whip) or higher SNEAK Attack?

https://ddb.ac/characters/18551769/F6QquX

I would personally say damage die.  It is consistent and scales with monk extra attacks.  Sneak attack can only trigger once per turn, and you likely won't get it for every turn unless you are sacrificing your bonus to use the inquisitive ability to get your sneak attack, which negates some of your potential attacks from monk.

Instead of Rogue use Warlock for Smiting Hex or Paladin for Smite for more damage instead of Insightful fighting?

You can just go straight monk, you will not be disappointed.  Never feel like you MUST multi class.

If you are looking for a quick damage boost, there is always a couple levels in fighter for Second Wind and Action Surge.  The bonuses for taking rogue would be the extra skills, not having to use ki for sprint and things like that as a bonus action as you get them from Cunning Action, Sneak attack damage when you have advantage from flanking or surprise, and damage reduction if you take rogue to level 5 (takes you reaction to halve the damage of attack).

I guess what kind of character did you have in mind when you started down this path?  Was there a fictional character you were trying to emulate?

I was thinking along the lines of Trevor from Castlevania (Netflix).  Someone who can do a lot more than 1D4 with a whip.

When I first saw Intuitive fighter I thought someone who, after watching someone fight know how and where to hit a target where he/she/it is most vulnerable.

If that helps.

I think that would make me lean towards doubling down on 5 Rogue 15 Monk (if you get that far) the uncanny dodge can be a strong tool to reduce damage taken from melee or spells, and you can use your monk deflect missiles for ranged attacks.  You get higher damage with that whip with its reach (handy) you can later on empower your weapon to become even more potent (very much like the video games powering up the vampire killer whip).  You will have a variety of weapons that you get the bonuses for as you continue to level up, which you can theme with some of the equipment that the Belmonts are most know for, Throwing Axes, throwing daggers, Darts (lots of thrown here, not saying you couldn't still pick up crossbow for longer ranges).  

As far as progression goes I would start as Rogue, gets you a few extra skills and then go for at least 3 in monk to get into your kensei subclass and give you access to the whip.  My personal opinion is to continue to 5 in Monk to get your extra attack and damage die increase,also your first ASI (at 4) which you will most likely want to stay with stat upgrades as you will want dex and wisdom pretty high preferably.  After that I think you are free to choose which class to level, an extra in monk gets you your next Kensei ability which makes your kensei weapons magical for overcoming damage reduction and lets you spend a ki point to deal some extra damage on a hit.  Or you take your rogue to AT LEAST 3 and then decide when you want your extra ASI from rogue, and later on when you want some more survivability with Uncanny Dodge (and another bump to the sneak attack die).  I think some of these things you will have to 'feel' your way through and decide if you like where your character is going up till then and choose your levels accordingly.

Have you made any decisions on what race you are going to go with?

I have a link to level 1 above.

That plus I do not need to go past level 17 in monk.  Any good 3 level dips

Fighter Champion:   Crit on and 19-20

Fighter: Samurai:  Bonus action to give self Advantage.

War Cleric:   Make an extra attack as a bonus action.  I know we have flurry of blows but to make another attack with a whip (10" range or ranged Kensal weapon me be nice) ((Help with Belmond undead hunter.))

Other ideas?

I would say pass on champion, Samurai might not be a bad idea at all, also War Cleric could be a good time if you want a couple spells to supplement.

Samurai for more up front combat 

Inquisitive for more skills and versatility

War Cleric for some spell support and allow you to use bonus action make an additional whip attack taking advantage of the range on it some more.