One thing we could do regarding rank and benefit is to allow a certain number of ship captains to start with a captain ability, and require that they come from the upper ranks.

For the French, folks have used the following schemas:

Contre-amiral
Capitaine de vaisseau
Capitaine de frégate
Capitaine de frégate
Capitaine de frégate
Capitaine de corvette
Capitaine de corvette
Lieutenant de vaisseau

Chef d'escadre
Capitaine de vaisseau
Capitaine de frégate
Capitaine de frégate
Capitaine de frégate
Capitaine de corvette
Capitaine de corvette
Lieutenant de vaisseau

We should settle on a given schema, and one roughly equivalent to the British. Basically, a lower level senior officer, several at/near captain rank, and a couple junior officers.