2 Core Sets + 2 of each small ship expansion (except for TIE Fighters, which you may want 7 or 8 of and the one TIE Advanced - there's just one Lord Vader, so...) + 1 if each large one is an excellent start!
On top of that I'd add a couple of bombers (they're much nicer when flown in 4's), a couple of Rebel Aces (so you get total of 4 B's and A's each), an Imperial Aces box (or two, for OCD reasons!) plus one of each huge ship.
With these you will have about 400 points (Team Epic) worth of ships alone on each side, before upgrades. This way you can also play with a lot more people who don't have a collection of their own but still like the game. Which is nice!
Anything above that is only good for collectors, modelers/painters or tournament players (who need 4 shuttles for the AS upgrade).
Edited by Iffo