You're hamstrung by Canon.
Maximals aren't slaves. And the Great War is over. A Maximal can do whatever they want to do. If they didn't want to be on that ship, then they wouldn't have been. This isn't Starship Troopers where one has to earn their citizenship with a stint in the military.
Rattrap - Probably escaping some kind of criminal charge for not so reputable transactions.
Cheetor - Youth, excited by the prospects of adventure.
Rhinox - Old hand, looking for a quiet ride around the Universe in peace.
Optimus Primal - 1st time Captain of his very own Starship.
None of this is 'canon' but can be assumed by what we learn of them and of their decisions during the course of the show.
Stasis pods always seem to be rigged with Transwarp cells when they're 'modified', but I'm of the opinion that they are already fitted with engines for planetary entry/landing and take-off. They sure as hell wouldn't all crash land - we've seen what happens when they do.
Rampage's was probably specially built as a prison. There is nothing in canon to say it was and there is nothing in canon that says that it wasn't, so canon, which you hold so much stead in, fails a lot. You've gotta take some creative license from time to time.