Hmm, I would start out with fighter vlass, due to the more HPīs you gain. After level ten this is just adding a few for each level so a 10th lvl fighter is good to have. Also you can always wonder about playing a multiclass character like fighter/thief. Trade off is the grabd mastery and higher points and you canīt choose subclasses.
To dual at tenth or twelth level seems to be a good choice, you wont like to stumble upon baddies as a level 2:thief...
I took the assasin to lvl 8 and dueled to fighter after that. Better weapon profiencies and a high stealth and you can still use thief boosting magic items and potions after awhile. Try some combinations out and see what they come out as...
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WOLF WINS EVERY FIGHT BUT ONE, AND IN THAT ONE, HE DIES