@NekoMizuLet's see if I can give a decent answer without spoiling more than I'd like to right now. For the most part, the information that people need to be aware of when making a character can mostly be put into two specific categories.
The first of the two things is basically character classification information, which basically stems from the fact that, in my setting, characters are divided based on what specific source they get their powers from, with their essentially being different classifications that allow for certain abilities and some that don't. The setting allows quite a lot of freedom over the powers a character can be capable of, but the specifics of how they are allowed to have them are usually where it becomes more complicated and without certain information about my setting people basically would not know what they should be registering as in order to make something possible. Of course, this only applies to people who want special powers. Ordinary people are obviously not denied entry in the story and can obviously be registered, so this first complication is only a problem for people who want to have powers, but as I've another person on this forum already through PM, one of the things my story is well known for among the people who follow it is how insanely powerful/broken some of the cast is. Sometimes the only thing preventing a character being a complete godmodder is that a lot of the characters cancel each other out in some way.
The other thing is basically connected to the setting of the story itself. A person's date of birth, place of origin, and some aspects of their history, will likely be effected based on the setting they are involved in, so obviously some knowledge about the setting will be required in order to register a character. Obviously, it's totally within my ability to make some of this information available in the GM post, so the main thing is working out which stuff needs to be known and which stuff is needless spoiler. At the very least, I'd need to give the primary history that led to the current state of the world, since this would, for the most part, be common knowledge for anyone in the setting. Thankfully, I actually have a history in my setting which is revealed right from the beginning of the story, and it doesn't reveal too much because, without spoiling, some of this history is completely fabricated.
For the most part, these were my major concerns. Apart from that, it's mostly just making sure I don't reveal too much of my setting on a public forum for the sake of copyright or spoiler reasons, since the only forums I usually use this setting on are private ones involving a small community, and also concerns I had that the rather heavy-handed nature of my story might be too severe for a public forum and I might break rules/guidelines here without intending to, but Lady Amalthea convinced me over PM that at the very least the last of those problems won't be an issue.
