A couple of questions from a new player.

[Niwashi]

Would I be gimping myself if I level different jobs on different characters (for example have one rogue character, one warrior character, one mage character... etc) too much, or is it a viable way to play?

As others have mentioned, it adds additional work to unlock everything repeatedly, but some players with a lot of time to spend on the game prefer to have their jobs separated out like that because some of the endgame content has weekly limits on loot you can get. They can gear up multiple jobs faster if they can earn that limit per job or per role, which is only possible if those jobs or roles are divided between different characters. (Where this is the main reason, the jobs are likely to be divided up between just two or three characters --like maybe all their DoW jobs on one character and all their DoM jobs on another. A character for each one would probably add too much lead time for anyone who's that focused on endgame.)

There are frustrations, like when you get a bound loot drop on a character who doesn't want it when you have another character who could have really used that. Having all jobs on one character means that, depending on level, you might be able to use the tank armour you got while playing your your rogue, or the Disciples of War boots that dropped while you were on your healer. You'd be giving up that flexibility in order to split the jobs between different characters.