[@HeySeuss]

I imagine interstellar communication has to be handled by ships rather than some FTL so it might take weeks or months for news to travel from the centers of power to the periphery. Dedicated couriers probably exist in the center which jump into system then beam transmissions to relay satellites. Outlying positions probably have a semi regular packet or naval dispatches carried on packets. Think of how news might reach Singapore or some other outlying possession during the age of sail.

The structure of the military is very similar to the Age of Sail British fleet, with the addition to the existence of a Naval Academy. You go to the Academy and are enrolled as a midshipman. Most commissions will be held by members of the aristocracy because those are the people who can afford an Academy education. It is possible for warrant officers to be commissioned but because this comes with a drop in pay for a senior warrant it is rare. It is also possible for heroic spacers to be made a midshipman and thus begin a climb up the ladder. It is rare, but there are famous examples. 

The overall mission of the ship is to keep the peace and fly the flag. I plan on having a Perdiccas II Macedonian style king who will keep the pot stirred up. Maintaining the peace might require placating or chastising local powers, building up informal alliances or any of the other morally questionable stuff that goes on at the very edges of Imperial power.

It is possible to profit from naval service. Smuggling is a thing as are any number of creative book keeping errors. There will also be prize money for the taking of enemy ships and cargo, similar to the British system, except with no distinction for privateers vs national ships. Recovering ships from pirates also results in prize money. There is all manner of scope for secret accounts for legitimate operations and private fortunes to be made if one is clever and/or unscrupulous.