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1. merchant in ars magicana w/ lost wagon. he gave me the wheel, then i brought it to the wagon, found the dead ppl, gave merchant the news. then he says he wants news on his wares?

Did you found the dead people or you found only the carrage broken? If not, you need to follow the blood trails. Once you arrive, you see a track of coins. Follow them but be advised: equipp yourself well or drop a teleporter stone in a safe place before venturing forth... If you are low level, of course.
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2. cabin w/o a door, near the cave where the robbers were. how do i get in?

East from that cabin there's a hollow treestump. Click on it.
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3. a guard told me about them wanting to catch the arms dealer? the one who sells the weapons in ars magicana.

It's related to the first question. Just follow the coins :0).
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4. how long do i have to wait for the animation in the cathedral. i see the lich hit the monk, but i think my game hangs after that scene... i can click and escape so that i can reload. i've tried 3 times, same result. it appears to have stopped, should i just wait it out?

Hmm... Looks like a bug. Better wait for Raze :0).
Good luck!