The Rebels rely heavily on their fighters, so definitely the fighter pack. Then I'd suggest to add Home One, an Assault Frigate and at least one more Corvette. With those you can play around and you can figure out which is your style that works with the Rebel fleet. With that you can pretty much discover anything the Rebels can do and you can expand your fleet according your taste from there.
thats what I'm doing to start out. 2 starter kits, a squadron kit, and an assault frigate. debating between adding a heros and villans pack or a MC30