You do need FFD for ground support fighters. I believe one FFD unit can control 6 fighters.
Correct. And because of this, and the fact that FFDs are relatively expensive as GUs go, building larger fighters for ground-support work is likely a good idea.
Also, someone said in another thread that ground support fighters need to have some kind of fire control, but that its quality really doesn't matter. I haven't tested this, but you may want to.