You probably won't get very far professionally sharpening using sharpeners at the Gatco/Lansky/KME level (unless you're thinking very small volume?). Guided freehand (non-powered) I'd look at the EdgePro (Pro model if you can swing it), or Wicked Edge. Most pros that do any volume work look at powered sharpeners... belt sander, paper wheels, Tormek, etc. Of course there's freehand using regular stones, although some of these sharpeners use a powered device of some sort for major work. But, as many in this forum have shown, it can be done quite successfully.
The website
Sharpening Made Easy has some good info on pro sharpening... even if you don't want to get into the setup he uses... it has a bit of info on various equipment, as well as some ideas for setting up a business... mostly related to sharpening at a farmer's market type venue.
If you're thinking of a mobile business, or looking at restaurants... you also might want to find out if there's a "knife rental" setup in your area... they're pretty tough to compete with price wise.