I’ve played in enormous fleet actions (sometimes involving enormous playing areas**) using Full Thrust. An excellent set of not overly detailed but loads of fun rules, and available now for free
** such as the village hall game we played in Bradley Stoke – the whole hall was the playing area, we had ships accellerating up to speeds of 50 or more at one point to get from one major area of action to another.
(You’ll want at least Full Thrust and Fleet Book 1, which changes quite a lot of the rules as well as having a list of pre-built ships. Fleet Book 2 gives you more ships and more weapons.)
One drawback to the rules as published, if you design your own ships, is that it can get a bit rock-paper-scissors: a fleet that’s all fighters and very light carriers can kill a conventionally-armed flight, which can kill an anti-fighter-specialised fleet, which can kill an all-fighter fleet. But if you stick with ship designs from the books or inspired by them, this shouldn’t be a problem.