Exactly! The Ark is MASSIVE so don't worry about making up places on it, and making up people is fine as well, since there's roughly 100,000 people on board, its fair game haha
Basically, do whatever you guys want to, and as you said, the RP writes itself.
I'm leaving this a pretty lax thread, I'll let you know if something should be changed a bit to follow the little guidance I plan on initiating, but other than that, do whatever you feel like!