I think it would be best to remain tightly focused on the fleets present in Klingon Armada. Add a few ships in CL40 that would round out the ones in KA, without adding new rules or races. My suggest ...
First on the list should be the Federation NCL, and also some "Middle Years" designs from the Feds and Klingons. This could lead to patrol/raid scenarios set in the "Middle Years" ...