What I mean is, if I want to run a dogfight with a few X-Wings vs a few Tie fighters do I need to buy a model to represent each ship? Do the expansions add an extra ship type, or just an extra ship?

I'm interested in getting the game, but wondering if I'm going to need to buy multiple packs to run dog fights.

Sorry if this is a noob question!

:)

Yes, you have to purchase model for each ship you want play with.

Expansions give you both extra ship types and extra ships.

Core game itself has a 2 TIE-fighters and 1 X-Wing.

Expansions are:

Wave 1:

TIE-fighter;

TIE-advanced;

X-Wing;

Y-Wing.

Wave 2:

Millenium Falcon;

Slave I;

TIE-interceptor;

A-Wing.

 Yes, you will need extra ships, you can't really proxy models in this game without having the extra unit cards, ship cards, and maneuver dials.

You don't need a model for each ship but you do need a base because of how maneuvering works.

There are multiple cards and enough fiddly bits for each ship type so you'd just need the base.

For example if you bought a core and a y-wing you'd have models for 2 ties, an x-wing, and a y-wing but you'd have everything you'd need to have 3 ties go against an x-wing, or 2 x-wings and 2 ties, or pretty much any combo of 4 of the ships. 

Still the models make it best and the expansions have unique pilots and upgrades and other little things that make them decent buys.

Bottom line, you can only play as many ships as you have bases, but you can mix them up more if you don't care about models.

To play the game as intended, yeah, you need to buy the stuff.

But for your own purposes you can proxy anything, including maneuver decisions. If I wanted to test out a 4 Y-Wing squad without spending a lot of money up front, I'd buy one Y expansion and and test out the other 3 using proxies.

 The most inconvenient thing about proxies, and the reason I don't play with proxies, is not having the right movement dial. I have 2 Y-wings at the moment. I'd love to play a 3-Y-wing game, but not having the maneuver dial makes it less appealing. Sure, I could just mark maneuvers on the sheet of possible Y-wing maneuvers, but it just isn't the same.