Is this a good dremel to use?

That's the model I use. It's good for simple jobs, but over time the battery can be a pain in the ass as you drain/recharge it. After awhile, the battery will die out very quickly, and the overall power on the Dremel will be lower (even after a full charge).

While a corded Dremel is much better, this one isn't too bad to start out. I've had mine for about 4 or 5 years, and it still serves me well enough (though far from perfect) after all that time of extensive use. I plan to upgrade eventually, but certainly would recommend that model to anyone just starting out. Especially if you only plan to do little work here and their for your personal collection.

As for the bit needed to hollow out heads, just scan down that page you posted. In the product description, the 2nd pic shows several bits laid out next to the Dremel. The one with green tip is what I use to hollow out heads (there's also a identical bit with a light brown/orange tip that works better if you can find it).

I usually just place the bit into the head, turn on the Dremel, and then work in a circular motion to grind out everything. Just work slowly, otherwise you could accidentally grind too much, and end up poking right through the top of the head itself. Stop every now and then to place the head on the body so you can see how things look.