You don't need any visa to buy a villa or rent it out as you won't be allowed to stay any longer than six months on a B2 visitors' visa or 90 days on a visa waiver. Most Florida home owners use the visa waiver scheme.

If you do want to live there and purchase a business, then you need to be looking at the info for an E2 visa (there's lots of info in this section and the Moving to Florida section of the forum) unless you have a current business in the UK (that you've had for at least a year) which you can leave running and for which you may be able to apply for an L1 intracompany transfer to set up a 'new branch' in the USA.