[@HeySeuss] Great! Its nice to have someone interested to help me articulate my ideas and hopefully add to my setting.

I envision that there are pockets of humanity that have become isolated through one thing or another. Shifts in the patterns of transit space, isolated and forgotten colonies of larger civilizations.  Some of these might have advanced, but I think more generally they will fall into barbarism as lack of contact makes high tech infrastructure impossible to maintain. fur clad hunter gatherers hunting in the ruins of fusion plants and the like.

Space battles tend to be settled without boarding actions. I haven't totally settled on space weaponry but I am thinking large torpedos which are fired from long range and maybe some sort of short range particle beams which can provide point defense and be used as weapons at close range.

In the isolated corner of the universe where the RP will take place there are a few regiments of regular forces and and native levies (similar to sepoys) who do the bulk of the soldiering but these are of poor quality due to long deployment in boring conditions with little cause to do more than bust up drunken brawls. Mostly they guard and police local bases. The quasi-independents might have all manner of troops...

Generally speaking if a problem is on the ground it has to be sorted out on the ground. Ship killing missiles and ground based weaponary can protect fixed locations from attack.

All ships are able to land and generally do land on water, to dissipate thruster heat. Shuttles, cutters and other small craft do exist, but it is possible for even the largest ships to land. Smaller ships are capable of some limited atmospheric operation, but firing particle weapons in the atmosphere degrades guns quickly, as they aren't designed for it.

Sorry if this is all a little stream of consciousness!