How big would the ACS vessels be in different scales? 1:1200? 1:2400? 1:3000? 1:5000? Are you talking just the Type S, Free/Far/Fat Traders, Gazelles, Fierys, Patrol Cruisers, SDBs and Corsairs? Were you going to include Kinunirs, Chrysanthemums, and other vessels of that size?
A Gazelle at 48m would be 40mm at 1:1200, 30mm long at 1:1800, and so on.
A Type R at 46m at the above scales would be 38mm & 26mm
A Type A at 35m again would be 29mm & 19mm.
I have some vague idea of the Chrysanthemum being about 35m long, just with quite a few decks. So that'd be something like a Type A above, just a lot chunkier and wider.
It would also depend on how many vessels were going to in use. If it was a standard PC's one-on-one then two or three is not an issue. If it was for escort-level actions involving a division of Gazelles, fighters, and a corsair flotilla then big miniatures made of white metal starts to become prohibitive.