Which officers are best suited for the different departments?

When viewing the different officers in the Gallery, you can click on the officer skills, and many of them read

"takes effect when assigned to _____ department"

or

"takes effect when sent marching"

You won't be assigning exploration or "marching" officers to departments.

click on their skills, and it tells you where to put them.

also, inside of the "command" building, each command tier will indicate which officers work together to unlock secondary skills, which can prove very helpful, provided you have the right officers at high enough level and star level. this is actually the only place where officer rank has no bearing.

hope this was helpful.