1) What class knows the most martial arts? Are they real martial arts like kung fu, or made up ones like krav maga?
Woops, I didn't make any martial arts-classes. Make your own or play a warrior or just play anything while formalizing a new martial art in-game.
2) Can I start out having already made a deal with the devil or do I have to do that in game?
By all means. Also, you can have the Devil as a godfather.
3) Do you want me to write an 8-page backstory? Can I write an 8-page backstory, if I want to? If I write something down in it like I'm the timelost princess of the brass city and the daughter of the sun and I commanded legions in the Hell War but was betrayed by my father's vizier but I don't know that, or that I'm elf conan and cooler than everyone else, will that be true?
Not necessary, but feel free to. I want nothing more than for you to play a timelost princess of your own initiative, and will work to make it happen.
4) If I eat someone's heart, will I gain their powers? What about their brain?
If they have cool powers, something will happen when you eat their organs.
5) These classes are boring, can I be one from somewhere else? What about from a different system entirely?
6) If I make a sword, which one of us gets to name it?
7) Am I allowed to kill the other player characters? What would I have to do to be allowed to? Do I win if I kill them all? Actually, how do I win in general?
That's a question for the group, not for the one player who's a DM.
8) What language stands in for 'Common'? Or what are we all talking to each other in? Like the party, mostly, but also everyone else?
In Mesomergos, Meso. In Holy Selmat, Selmati. In Okucenza, Tengor.
9) How do I learn how to talk to rocks? No not once a day just, like, normally?
It's on the list of starting languages.
10) Which kinds of wizards get to serve kings and live in towers and shit and which ones are run out of town or stoned to death in the streets? Can I be both? At the same time?
Honestly, it's usually both. Lot of Simon Magi in these parts. Having magic isn't taboo, being a heel is.