depending on time, effort and future changes to build limitations there would be the following races
the republic is the tough one, all of the other factions have a short histroy or very few ships to begin with, the republic has a decent amount of stuff from the KOTOR eras and then in the clone wars, still have to figure that one out. This is a lot of work to get to this point (lots of importing and bug fixing as well as a handful of new models and textures that I need to put together) and it REQUIRES IronClad to change some things about how the build queues are handled.
as for the current upcoming release I have discovered the problem and it is the nebulon-b, to speed release I will omit it from the build menu (not a big loss)
for testing I have run a large 8 player galaxy with 8 AI players at 8x speed multiple times and it doen't crash so I think it is stable enough to play. I may release on the 21st or the 23rd depending on the time I have.
for the mandalorians they have the basilikan battleships as well as the Mandalorian DreadnaughtKedalbe battlecruiser
and IMO the Aggressor Cruiser
so they would have at least a few large ships, nothing spectatualy large though, but neither would the sith they would be paired with, but they would have lots of completely awesome abilities.