It would probably be hard to estimate that but any rescue can be as big or small as they have the funds to support. I agree with PPM, start small, figure out what your base market is and go from there. Make sure he's willing to put feed, time and training into each and every horse he takes on. Start with two or three, fit them out, sell them, and get a feel for your market. re-invest your profit (if any) into the next two or three etc...