I suppose I'll throw out a few ideas for merging Babylon Five cultures with Trek ones. I hope some of these are useful in some capacity, if you feel like using any of these races
. Forgive me if I've misunderstood your particular concept for the merger, but if we're having B5 cultures inserted into the Trek-verse...
: Their government is corporate-based, so you could have them as the driving force behind a League of Non-Aligned Worlds equivalent, based around economic power and control of trade, perhaps in concert with the Rigelians and Orions? The Rigel system, like in the regular Trek verse, is a leading economic lynchpin of the region and a major trade hub, only the Brakiri have made them a bit more proactive, and they send trading fleets or pirates to other systems instead of mostly inviting everyone to come to them? The Orions are far less decentralized because the Brakiri have integrated them into their corporate structure? Instead of joining the UFP, the Rigelians become an economic rival? You could "vacuum up" established Trek races that wander the spacelanes but seem to have little centralized authority - Orions, Nausicaans, Yridians - and make them members of an organized Brakiri empire? The Llort,
the armadillo-cow people on B5 who never say anything, are known for their loose grasp of property and their hoarding of items that have caught their fancy, so maybe they could be part of this, too? The Rigelian/Brakiri Alliance...like the Ferengi Alliance, but far closer to Earth and the other UFP core worlds, and both a tempting ally and a threat.
The Abbai, Hyach
might all be good candidates for UFP members. These societies are generally peaceful and value diplomacy; rather advanced technologically, but defensive in their military applications rather than aggressive. The Abbai certainly would be involved in any attempt to create a community of worlds, and the Hyach would follow, though more warily due to their shame over the Hyach-do genocide (they don't want to reveal too much). Maybe the Hyach are allied with the Vulcans? They're reserved, orderly, respectful of age and wisdom, and hide a few dark secrets. Maybe the Vulcans and Hyach are partners because they see themselves in each other? As for the Abbai, the Interspecies Medical Exchange was probably their idea, with Denobulans, Tiburonians, Vulcans, etc, agreeing to support it. The Yolu tend to be isolationist, but might be tempted out of seclusion if approached openly.
If the Minbari are part of the UFP and Earth's first contact, why not have later UFP members like Deltans, Efrosians, Bolians and Benzites be protectorates of the Minbari, corresponding to the races that form the Minbari Protectorate in the actual B5 universe (who were mentioned and one of them named, but never seen?) That way the UFP can have a full membership due to these peoples all following Minbar in. It will emphasise that Minbari are a true power and serves as a nice way to get those various later Federation members into the mix. And you can kill two birds with one stone by answering the question, "where does Minbari space fit? Why, over the territory where Delta, Bolarus, Benzar, etc, are found". Betazed might go here too; after all, a planet of telepaths is clearly a Vorlon petri dish of some sorts, isn't it? Minbari territory is a good place for that.
might be part of the Klingon Empire? The Klingons conquered Drazi space, the Drazi fought well but were defeated, the Klingons recognized the courage and tenacity of their foes and incorporated them into their ranks? Drazi are brawlers, not warriors, and as conquered people couldn't be high-placed in the Empire, but perhaps the Klingons approve of using Drazi as their thugs and bodyguards, leaving the "nobler" bloodshed and warrior behaviour to actual Klingons?
are, of course, everywhere. In B5, their homeworld is the source of much of the Quantium-40, so I assume they're swimming in dilithium in this universe. You could have them in league with, or as rivals to, Coridan. Coridan was a flashpoint between Vulcan and Andorian in the real Trek verse, and 100 years later a point of dispute in the UFP, so having pak'ma'ra as agents or spies for Coridan, struggling to stay afloat as it's caught between the local powers, might be a nice angle.