Can i make a suggestion, on the mod i was on (Freeworlds Total Conversion) factions had to go by a limit rule.
It was pretty much like this, factions could only have these online at one time.
One battleship
3 Gunships
3 Light caps
Thats how it worked on that server, here it would should be like,
Every faction would have to abide by this and it would have to be a server rule i think.
But each faction would be allowed on at one time,
1 Battleship
2 Destroyers/Cruisers
2 Gunboats
The rest would have to be fighters/bombers
(The Brotherhood has a similar rule)
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This rule worked very well on there server, the only thing it wouldn't stop is the independents, who fly battleships.
The thing that Freeworlds didto counter that was to only let "independents" (People not in a faction [Civs]) them use ships up to a Cruiser or maybe even Gunboats.
Because as it stands (Roleplay vise) individuals wouldn't be able to buy a BS or even man one.