I've never set up any type of shopping cart before. Which is easiest to set up and use?

Check with your hosting compnay as they may already offer one in your hosting package.

Open cart is easy and a nice little cart

I work for/with E-Junkie and it's super easy to use/setup, and it integrates with PayPal plus other payment processors so you can offer more than one payment option for your buyers.

If you're code savvy and not interested in digital delivery, E-Junkie's free solution is FatFreeCart