1.) I don't think very many people would have problems with a demon-hunting samurai. Voidsent are a common threat in Eorzea and samurai is a common profession. Not to mention, you don't always have to be a specific job. My main character uses a gunblade, but she isn't a gunbreaker. She's just a warrior (in the generic sense of the word) that just so happens to fight with a gunblade.
2.) As mentioned Encyclopedia Eorzea. There's a few wikis that have some extra bits of information... Or at least information that exists in the game that's more easily accessible.
3.) I think this tends to be how most people role-play in Final Fantasy, both in-game and on discord.