[Stilgar]

First Welcome to the forum.

I can recomand first doing some easyer quests before going into the sewers.
Some quests in the city, and the crossroad quests arent to hard either.

I'm not very far in the game myself, but I think magic is pretty importend (more then half the skills are magic).
If you dont want to be a combatcaster, just pick some of the protective branch.

You dont have to kill the beggars, you can side with them against the thieves (or side with the thieves against the beggars) (note that the beggers have better rewards)

Did I forget anything?

Good luck