So  i have been stealing from NPC's from time to time and i get some stuff but i sreach and i cant find alot of info about this mechanic
Any of you know the steal drop and what all the npc may drop or are there any achivments or something to achive?

And have you steal from them and if you do what is the best stolen item you got?

Mine was a potion that sell for 93k 

That's a good question and honestly I have no idea since I have never seen a website dedicated to this. I don't know if this is reliable but:

https://bdocodex.com/us/stealable/

I doubt most items there can be stolen like 1st anniversarry stuff? Doubt it. I've stolen housing items from NPCs somehow. Don't ask me what pocket they were keeping it in. Would be interesting if certain NPCs carried certain gear and you could join a thief's guild of some sort. Special gloves could be worn to improve pick pocketing changes etc... I'd be game to play that.

I once got a cauldron on a mounting arm from Gahaz Tuval.  Dude wears very large pants, I guess.

It will be so fun to get in to a thiefs guild and like some sort of base and daly quest's to stael from npc's like in the elder scrools online 
And to be a part of the life skilling ohhhh ohhh this gon be so good :)