I am 16lvl thief, I do use both bows and daggers. I got question about armors, should I level up blacksmithing and make dragon armors even they dont have any bonuses as DB's and thieves guilds armors have.

I wouldnt

if you're playing stealth i wouldnt worry about armor rating just magic res. only dragona are gonna see you...

Yeah, I would focus more on sneak and archery than armour. Maybe get a tank hireling if you wanyt, otherwise (ideally), your enemies won't see you until they're dead.

Okay, not gonna train blacksmithing then.. But alchemy is good for thief?