If you want a control surface and you're going with Pro Tool, go with the Digi003. There's also, the Command|8 (I'm happy with mine) and the C|24, as well as a few other third party control surfaces that work with Pro Tools.
The first thing would probably still be to understand the difference between a mixer and a control surface - the former mixes audio signals internally, usually down to one or more output pairs while a "pure" control surface doesn't have audio signals going through it at all; it just controls the software where the signal summing is being made. And then there's hybrids of these: the mentioned 003 is not really a mixer, but it combines an audio interface into a control surface.