Hi and welcome to Eye on Spain.
I live in Manilva which is about 30 minutes from Marbella and in December hurt my back really badly. Trying to find an osteopath was a little tricky mainly because around Marbella there were quite a few and I didn't know if they were any good or not.
I ended up going with a recommendation based near Sotogrande. He told me that business was great for him but I think it's because of his location and reputation. He's also very handsome and hence popular with the ladies, which probably has something to do with his success too
There is a Spanish website that lists all (or most) osteopaths and chiroprctors in Spain so that is probably a good starting point for deciding where to go.
In terms of buying and renting...I think the rental option would be best just in case you can't make your business work in one area you can then just pack up and try again somewhere else. Much easier to do when renting.
Best of luck with the move.
Justin