Um, again, weighing in with my own opinion here...

IC it doesn't matter if the character is canon or not. No-one should know their identity to start out, unless they go on blabbing it or do something that would reveal it. It doesn't matter if they're canon unless they've been summoned in a previous war [i]and[/i] the character determining their identity knows they were and who they were.

Balance issues aren't always easy to judge, especially given the only way to convey a GM's vision for an RP's balance is really for them to just try and describe what they want. Complexity and amount of related conditions makes it harder to work out how they would interact with other characters in terms of balance.

Again, not GMing, I just... really want this to be fun for people and for there not to be heated arguments or anything like that. I've seen way too many Fate RPs end up with arguments including when I try to run them and it's kind of upsetting since it's such a fun set-up for an RP.