Hey, welcome to the forums!
I don't know if it's just me, but the merchant skill isn't a skill that I'd use much. From what I have heard, by the time you're playing at lv 30, you'll have more gold than you can deal with and you'll end up buying two of every single item in the game, and still have enough gold to buy everything in Andor's trail ten times over. So, if you plan on sticking to this build for a while, I'd suggest getting a skill like regeneration or, if you don't like waiting around for hp, corpse eater.
About what to use in lv ups:
From what I see, you prefer to be the guy who attacks first and attacks last, i.e., ending the battle as soon as possible. Criticals are good for this purpose, you just have to find the right weapons for it. There are three best critical weapons in the game, and I shall list them out now:
So, if you plan to keep the critical chance, I recommend going critical all the way, or it would be pretty useless to have only 5 critical hit skill and no critical multiplier.When in lower levels, I think it is best to develop extremely, i.e., all AC, all AD, all BC, et.c. So that's my advice for you, and happy hunting!

Hey guys, I'm back.