If you're asking the kind of questions that you are, I think it would be best for a Foundation Pro or an Excavation Pro to at least do the footings/piers and foundation. It's not a simple matter of digging out dirt. As you've realized, the home needs to be shored and then the digging can begin.
I think from there, assuming you're handy enough, you can proceed with the work after the foundation and floor is poured. Consider installing drain tile, having a vapor/moisture barrier installed BEFORE the floor is poured, and possibly even either a center drain (or corner drain), and if necessary, a sump pump pit. I'd look into a 10' UNfinished ceiling too. The Pros will go over all this w/you.