Download and configure Centauri Vaughn's Spawn and Fleet Pick scripts.
From out of game, you can set up Spawn with the race and ship classes you want, and the amount of waves, and it will start spawning waves of enemies. You can have up to 6 players/AI allies, and there will be as many waves of enemies (including infinite!) as you decide. Each wave will have 2 to 5 enemy ships.
The greatest battle I've ever played was when I me and a buddy (multiplayer skirmish) did Spawn...us in Defiants, with 4 other Defiants...and I had Star Wars ships spawning everywhere. I ended up against 5 ships varying from CL to CA size...then an SSD spawned after we killed them
Funny thing was to do that same thing in an Asteroid belt...SSD spawns...SSD panics and spins around...SSD hits asteroid...SSD blows up. Death Star spawns...Death Star panics and spins around... Death Star hits an asteroid. I laugh. Little ships attack me, and I burn through them.
Hehe.
As for Fleet Pick, you can set it up with something like 10 AI (you pick the ships!) to fight, then go in game and you can pick the 6 ships you want to do the mission with. The result is a grand total of up to 16 ships for the mission.