So my friends and I want to get into IA, and knowing I'll need the base game and expansions, what should I look at buying for Skirmish? I would probably want to play Scum, and the only figure I own is Chewie from a joke gift. Thanks for the help in advance!

If you want to play Scum, you'll probably want Boba, he's a great unit. The HK's and Wampas are also really good, and those both come in the Return to Hoth Set. And if you get that you're starting off with Core + Hoth and Boba, which is enoguh to play around with for a while.

Hired guns are also cheap good fillers to run objectives and mess with opponents target priority

Hired Guns are fantastic, good value for the points. As is Fett.

For Mercs, you almost need to supplement in rebels through Temporary Alliance. So, Leia, 3PO and Rebel Saboteurs are really good as well.

Look through threads here to see how people are making mercs work.

The best merc units hands down right now are regular HK assassin droids. Problem is only one set of those comes in the return to Hoth expansion so if you are looking to not buy a couple of the same expansion Tuskens and Hired Guns are decent to get you started and Boba is always fun to play(Although a little pricey at 13 points) the base set comes with Nexus and both of those are viable though I favor the elite slightly.

Like Zhsalt above me said a lot of Merc lists run a splash of rebels to give them an extra hand. Gideon and C3PO are great options there to give your units focus all game.

Wow, thanks for all the help everyone!