Diamond: Small, lightly armed and a transport- fit's the bill perfectly for a light carrier.
Trident: not sure given that it seems to be primarily aquatic. Wouldn't the arms be difficult to animate? (if locked in place, what position?)
Umbaran support ship- wouldn't that be restricted to Umbara? As far as I can tell its in the same rare category as the munifex.
Separatist cruiser- No canon armament but that might not be a problem.
The diamond and separatist cruiser look like the best bets as far as I can see.
I'd say the Diamond is fairly well armed for a transport. 2 forward facing laser cannon batteries and 13 laser cannon emplacements. Could probably do some anti-fighter stuff if it had to. I don't think it has a launch bay for fighters though.
Warb_Null had no problem making the "arms" animate on his. I have no reason to believe it would be difficult for the team. We have seen them operate in space though we have not seen them in any space combat situations.
Maybe, but I would have also thought the Munificent would be restricted to Muunilinst for the PA in ICW, but it's not.
As for the Separatist Cruiser, we can see what appears to be a laser cannon or turbolaser cannon at the bow of the ship. The main thing working against this (that I can think of) is next to nothing is known about it.