Each character in the party has a distinct personality and slightly different goals. I foresee this causing future party splits where one person wants to take care of a personal goal.
So…
This is a system a former GM of mine used, and it worked reasonably well. Essentially, everyone can roll up a secondary character (or claim an existing NPC with GM permission) that is associated with the party. If your main character wants to do a side quest of some kind, rather than try to run two games simultaneously, you simply have your main character go off for a bit and play your secondary character instead.
Secondary characters are 2 levels below main characters in level, and then level when the main character does. Otherwise they utilize the same character generation rules. If your main character dies, the secondary character can be elevated to main character status.
This system does require absolute trust regarding metagaming. Your characters have separate brains. It also requires some rationality, if the party is in say, a dungeon in Tatsuo and your main character wants to explore a side tunnel, your secondary character can't just pop in.
I've seen such a system work well, and I've seen it be an utter disaster. Thoughts, questions, comments, smart remarks?