Gorns all the way - what's a defensive phaser, Plasma Torps and love the background for the Name of the 'Godzilla' Heavy Dreadnought (when they built it, they were gonig to call it the 'Mega-Rex', or something along that line. A Federation officer saw it, and called it Godzilla. Gorns asked him to explain - they approved, and the name stuck)
Next fleet would be the ISC, then Klingon.
Yes, the Romulan's, used refitted Klingon ships, but if your going to stick to 'on screen' ships, you'll miss out on the 'Hawk' class new destroyers/crusiers.
I was a long term B5 player (Drakh), and have been into SFB/FC for a long time (20+ years). SFU will nicely fill the 'grand fleet' option, as even FC can have issues with lots of ships, even at 'Fleet' scale.