MLS will never do well in Florida. There is simply too much else to do there, and whether WE like it or not, soccer is very much still a niche sport in the US. The NFL does well in Miami and Tampa. The NBA does well-ish in Miami and Orlando.. but look at MLB. MLB was very late getting into Florida and both the Marlins and the Ray have always had attendance issues. Miami couldn't even sell out a world series game a few years ago. The NHL can't draw flies down there either, except when they give tickets away. About the only cities in the south that are capable of supporting MLS are Atlanta, and possibly Charlotte. Nashville would be a possibility also.. but an iffy one.. at best.
I'm not a football manager, I just play one on the Internet.