I don't know if having a medium Imperial war fleet from the United Empire of Mankind would make sense or not or even work at all, but why not, maybe the fleet got jump drived into this universe by accident. If you want to add it as some sort of support or onslaught army here are dimensions of a medium imperial wartime fleet:
3 Dreadnought class ships ( referred to as a "Chariot of Man" Class in the Empire, both capable of carrying strike craft bays and Mammoth Drop ships as well as gunships. Around 3000 soldiers per ship, and 1200 vehicles (low-key made these numbers on the spot, adjust to liking))
5-7 battle-cruiser class ships (can either hold armies, or be modified Into a Regulator class, a orbital bombardment specialised variation)
10-20 Corvettes and or frigates (corvettes can be modified into pickets, sniper variation of a corvette, and frigates are used as torpedo ships, but can given a spinal mounted lance cannon for ship killing, though that may not be nessacary)
I'll have to read the story fully to get an idea, but just throwing this out here for fun. 😅✌✨