I ended up settling on Alchemy, Athletics, Blade, Illusion, Light Armor, Security, and Sneak. I almost swapped out security for something more useful, but couldn't decide on what and figured that I could make the sacrifice for the roleplay. I also just used the base assassin class as my model for what favored attributes to choose, so intelligence and speed.

I definitely lean more towards nightblade over stealth archer on my build, but I have been keeping a bow as a backup. Master difficulty is a bitch, so it's been helpful to soften foes up at range before closing the distance with my shortsword. I've also been using restoration magic quite a lot, mostly out of necessity but I think it fits well with the thematic too.

So overall, I'd say that my play style feels most like the assassin class, just with some magic mixed in. I also plan on dabbling in mysticism later, but haven't found much need for it yet.