Question 2.

Does this description fully capture the requirements for playing the game? Are there any additional rules or assumptions that you may have left out? Do these need to be written down? Why/why not?

There's one part which I left out, and that falls under the category of "Role". While I described a bit about your character's role in the story, I didn't mention exactly what sort of person your character is, or what race or class or even gender you had to play as. Here's the thing - you get to choose. You even get to make up your own backstory while you're at it, because I wanted to give players the freedom to do that. Want to be a grumpy little dwarven fighter? Or a chaotic evil halfling rogue? Or a sarcastic elven ranger? Go ahead. It's all about choice.

During the trial, a couple of "evidences" show up, and the game only tells you that one of them isn't true. You're not told whether the other is true, and you're allowed to argue it any way you like. Even a response like "Erm... that was my evil twin, not me" can either be treated as a lame defence by your character, or as the truth, since it was stated in the journal entries that someone's impersonating your character while you're in Hell in order to harm your friends.

Why I don't need to explicitly say that you're free to roleplay is because the mod belongs to the RPG category. The name is self-explanatory. You pick a character you want to play as and you roleplay it.