Well as far as my humble understanding of this thing goes here are the answers to most questions :

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 1: pretty much 1 char per player.
2: for the world building you just need to make sure you get the thumbs up from the gm and then make sure it doesn’t clash with anyone’s things
4:not really humanoid races, this is humancentric. You need to look human enough xD
5:it would be preferred to read through it, cause it is pretty cool, but in few words, heroes and villains get resurrected to fight big evil dark thing that killed all the gods and will probably devour the world or something like that xD
6:that should be the GM. He also plays a pretty good mystical ancient tree that talks in riddles! 
7:ehhh not completely sure about this one. As far as I understood it gods exist in the same real as the humans and heroes or at least some of them. The goddess of my character for example was killed and left to hang on a tree, so the insects and crows can feast on her body
8:discuss this with the GM. Some of the characters already have tagalongs *shrugs*
9: About this you need to talk to our good ol’ GM! He is the best!

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[@Vigfast] bloody hells, you got the better of me! Just before I post too! Good job on the timing xD

EDIT: opps... missed a question there. fixed the numbering.