Remind that Discovery isn't a MP mod only. Some peoples like me enjoy to explore the Discovery universe in open SP and try all the different ships. It will be very hard if the capships and MkII Fighters been sold in guard systems only.
For RP the player should get the permission of the admins to buy a capship. Dependend to the military ranking indifferent of lawful or unlawful. Only Admirals should own a battleship. Rear- and Viceadmirals or Commodores should own cruisers. Colonels/Commanders own destroyers (I'm for splitting cruisers and destroyers into different ship classes dependend to their specific strategical and tactical tasks). Their must be special deployed bomber groups with a limited number and so on down in the hierarchy.
The greater factions only should have one or two admirals on movable BS, three or four Rear- and/or Viceadmirals for example. Means there are no Admirals along with Xenos, Gaians and other small factions.
Civilians must be unable to own a capship except for the Bountyhunters. Freelancers should own a Gunboat at the maximum.
I'm not experienced in Discovery RP, but i hope you can catch my drift. I think not all i suggest is nonsense, cause its the way i would manage the RP aspect. Especially to avoid a capship rush.