I feel like deploying the Odyssey (which looks to be getting a boost to Veteran) is enough to deal with Caldonian space in addition to the ships we have in the KBZ. If we did not want to do that I could then see sending in the Andorians but since we are sending in the Odyssey they are not as likely to help.
Given Sulu's bonuses, sending
Voshev might better than sending any other ship we have. Sulu gets rerolls on diplomacy tests in Federation space, and this may qualify. Sulu gets +1 Presence. Sulu gets +1 to espionage rolls, and some of the missions she undertakes may qualify.
I wouldn't hesitate to trust Sulu and the
Voshev with this task.
I feel member world overcommitment to Gabriel could unlock a Southern Strategy for the Cardassians. Not that UE to GBZ would automatically do that, but to explain...
Deplete the member fleets enough and a flanking thrust from Lecarre (likely) or possibly Dawiar (remote) space becomes viable, which would occupy the Caitian Grand Fleet, the Qloathi fleet, and remove an entire vector of reinforcement for the Indorian triangle. We'd have to reinforce against a southern push from our original four, which could delay response to an attack on Lapycorias/Indoria/Rethelia until too late. The Cardassians could easily ignore forces in the Gabriel in exchange for this, and shifting our GBZ fleet south isn't going to be quick, especially if we're expecting a northern blow too.
I think surging the Gabriel makes some sense now, but I must caution staying so heavily committed for too long.
The big problem with this strategy is that it relies on one of two things happening.
1) Us not having time to redeploy forces out of the Gabriel Expanse back towards our own space, prior to the Cardassian attack. This is a valid assumption if we anticipate a "bolt from the blue" attack, but less so if we anticipate an attack that takes place as a reaction to escalating tensions that build up over the course of a couple of months.
2) Alternatively, it relies on the member world fleets
actually losing ships in the Expanse so that they are materially weakened. This does not seem to be happening, and if the Cardassians plan to make it happen, they have to launch a major offensive in the face of coordinated defensive action by a very large force. Plus, they'd be attacking with their own core fleet, not with relatively expendable affiliates. This is a problem for them, because the ships they'd use to grind us down in the Gabriel Expanse are the exact same force they would later use to threaten Lapycorias and Indoria.
Furthermore, the member world fleets are going to get stronger rather than weaker
in the long run because of the Gabriel Expanse. The biggest limit on the Apiata fleet is resources. If the Apiata find any special resource colonies in the Gabriel Expanse, that translates directly into more Stingers. Even bulk resources may, because as we've seen, the Apiata can trade those bulk resources to people with SR surpluses elsewhere in the Federation sphere of influence.
Now, I DO think we have a problem with the relative level of Starfleet commitment to the Klingon/Romulan/Cardassian Border Zones, as opposed to the Gabriel Expanse. Arguably we should be taking the ships of that third Starfleet task force in the Expanse and instead distributing them to the other borders. I think that's a policy debate we need to have during 2316, because you're not wrong to worry about us failing to properly secure the borders that directly protect our member worlds from incursion, due to having so many ships off in the Gabriel Expanse.
After all, beyond a certain point, our ability to find new colonies and grow in the Expanse is going to be limited by the available engineering and logistics infrastructure,
not by the mass of armed starships we have available. Unless we're planning a massed fleet assault against the Cardassian outposts and starbase (and that could get very bloody), we can only accomplish so much.