In the long run, if you were thinking of expanding further into the setting, there are a number of additional options out there.
The first I might mention is
Feeration Commander: War and Peace, which adds the
Vudar Enclave,
Inter-Stellar Concordium, and
Andromedan Invaders to the game system.
The Vudar are a "special case" Klingon subject species with a range of ion-based technologies; the ISC lies on the far side of the Gorns and Romulans (from a Federation perspective); while the Andromedans are mysterious extra-galactic invaders with a slew of unique technologies available to them.
The rules needed to fly Vudar, ISC, and Andro Ship Cards are in the most recent update to the
FC Reference Rulebook.
Beyond that, there is a PDF preview pack for a pair of "
lost empires": the
Carnivons and
Paravians. These two species were introduced in
Star Fleet Battles'
Early Years modules; a "what-if" set of "modern" ships was published in
SFB Module C6, showing what their respective fleets would have looked like had they remained a factor in the Alpha Octant.
(On a side note, there is an
FC preview of sorts for the Early Years setting in
Captain's Log #39 and the
CL39 Supplemental File.)
The Carnivons are a wolf-like species distantly related to the Kzintis and Lyrans; historically, they were defeated and subjected to mass xenocide by their feline cousins, but reports indicate that a "last command" may have successfully fled to the Sargasso Storm Zone. The bird-like Paravians are genetically related to the Gorns, but grew a pathological hatred for their reptilian kin; their home world was wiped out when a Sun Snake (a kind of "space monster") drove their home star nova, but a group of survivors managed to flee to the distant
Omega Octant.
(As shown
on this galactic map, the Milky Way of the Star Fleet Universe is divided into twenty-four sectors, which in turn are split into five regions amenable to "life as we know it".)
Speaking of Omega, there is a playtest pack available for that setting. Things work quite differently over there relative to the Alpha Octant; while the empires currently previewed in
FC all use "metal-hull" starships, other, more exotic factions lurk over in
SFB.
There is another playtest pack for the
Lesser Magellanic Cloud, an "island galaxy" which the Andromedans conquered in the run-up to their assault on the Milky Way.
(As a disclaimer, I should note that I wrote the rule portions of these playtest packs, though they are based on modules written for
SFB by others.)
And if you ever decided to give
Tholian Attack a second look, it includes data on how to do battle in the M81 Galaxy (the Tholian and Seltorian "home galaxy"). There is even a pair of black-and-white Ship Cards for the M81 Pirates in
Captain's Log #40, which work very differently to the Orion Pirates in the Alpha Octant - or, for that matter, to the respective "pirate" factions in Omega and the LMC.
There are playest rules and Ship Cards for two "almost-were" empires in
Captain's Log: the Peladine (who were conquered by the Lyrans) are previewed for
SFB in
Module E4, and for
FC in
CL50; while the Borak (who were absorbed by the Hydrans) are previewed for
SFB in
Module E3, and for
FC in
CL51.
Beyond all of that, there are even more empires, eras, and settings which exist over in
SFB- not least of which being
first-generation X-ships.
And the prospect of new modules for
SFB itself, such as
Module X2 (a new generation of advanced warships), or a module looking at the Xorkaelian Tyranny (the empire over on the far side of the galactic map, which is set to become the "big bad" of the X2 era).
How many of those may one day end up in
FC remains to be seen.
Of course, with the possible exception of
War and Peace (which is the only one of these to be formally published, in terms of having a "full" module with countersheets and laminated Ship Cards included), any and all of the above are strictly optional. But still, if you were to find yourself wishing to see what else is out there in the broader game universe, there's a healthy range of options to consider.
Oh, and if you haven't seen it already, I'd recommend taking a look at the
Commander's Circle, and the back issues of the free monthly
Communique magazine. There is a lot of material there which may help you get settled in to all this game system has to offer.
Plus, if you haven't popped over already, it might be worth taking a look
over at the Discus BBS.