Up and coming cities...

I am a 16 year old living in Toronto, Ontario, Canada. I have a great interest in cities and I am almost positive that I want to take Urban and Regional Planning in University when I graduate high school in a couple of years. I realise I am looking too far ahead, however I have always planned to eventually start my own condo conversion or development business after I have worked in Urban planning for a few years, and have gotten to know the city I work in inside out. Well I do love the city of Toronto, I feel it is way too big and developed already for someone like me to start off small and work my way up in as a developer, and that I would be better off going to a smaller city that appears to be real up and coming, with a bright future, especially for downtown development. (Please correct me if this theory is wrong)

Therefore my question is, what U.S. sunbelt cities should I be starting to think about looking into once I have my Masters degree in Urban Planning (since I want to start off working in planning in the same city I will eventually be developing buildings in) Like I mentioned earlier, I want to be looking at smaller cities, or cities with small or empty downtowns, which look like they could start turning around and promoting downtown living and development in the next 10 years or so, so that I would likely be able to ride the front of the wave once I have graduated, and worked in planning for about 5 years or so. (So probably about 10 years from now) I realise that it may be too far away to tell, however I am just looking for some possible options. Also, I am looking for cities in the U.S. with a warmer climate.

Thanks in advance.>