I have a small Wacom Graphire, my first tablet. I read somewhere to go small and see how you like it, how you use it, how often you use it. This way you're not out of a lot of $$ when you discover the smallest is perfect for what you need. I've had my Graphire for 3 years now, maybe  a little more. I'm just now thinking about upgrading to a slightly bigger one. Since getting Vista, it's doing weird things such as working in close up mode, the thing constantly wants to bring up the brush size menu. I didn't have a single problem with it in XP.

Right about the mouse. Mine came with one and I never used it.

As Pjz99 stated, look at your desk and see how you would use it, how much space you have. One thing to keep in mind too, do you have children and animals like cats. Slightest scratch on the cover can really mess things up. So you'll want to keep in a safe place for it when not in use, which could also factor in what size you want to get :)