Disambiguation: I assume "Platoon" refers to the Navaho's marine/infantry unit?

In a real world navy, the titles of Captain and 1st Officer aren't automatically tied to the officer's rank. A Lieutenat can be addressed as "Captain", if he's the commanding officer of the ship, as is often the case for smaller vessels. * That shouldn't be a problem with a ship as big the Navaho though. **

"Spaceman" might be a specific title granted to cadets who complete a series of tests, to basically prove they can be left unsupervised and not accidentally kill themselves. Might also consider "Spacehand" as a more gender neutral term.

Other than that it all looks sensible.

* And if an officer with the rank> of Captain comes aboard for any reason, sometimes they get a courtesy promotion to Commodore for the duration of their visit, to avoid confusion with the vessel's commander.

** I'm also mildly amused that a Vulpine vessel is named after a tribe of native americans, but I'm sure they can appreciate anyone who fought an armed resistance to another power trying to erase the former's culture.