This is a great post.
We are currently in the process of exploring possible relocation areas as well. Our current plan is to remain in our current home for the next four to five years while we continue to build our stash. In the mean time, we are slowly exploring different areas of the country.
Like the OP, we would like to move to an area that has warmer weather (We currently reside in PA), but it isn't a top priority for us. We are also attracted to smaller to mid sized cities. Our list of priorities goes something like this, with the most important at the top:
1. Bikeable/walkable: We currently commute by car to work (30 minutes and 50 minutes). I wouldn't mind part time work when we FIRE, but I would like to bike to work. In fact, It is a top priority that we can bike and walk to as many places as possible. We currently utilize a rails to trails type bike path that connects us to other communities in the area, but we would like to expand our abilities to utilize our bikes as transportation. As a result, this is on the top of the list for us.
2. Crime rate: I think this is self explanatory, so I won't elaborate further.
3. COL: We currently have a low cost of living. We live in an area where home prices are not too bad. We have no mortgage and taxes are fairly low. Our overall expenses are pretty low in general. As a result, we could handle a slight increase in COL if it gets us in the right area.
4. Weather: We would prefer warmer weather, however, as I explore further this keeps moving up and down the priority list.
5. Schools: We don't have children, so school systems don't hold as much value for us
I just recently a started process to get more organized with my search. Since bicycle friendly places are currently a top priority, I decided to start making a list of places based on its ranking with the League of American Bicyclists. Here is a link to their community ratings if you are not already familiar with it:
http://bikeleague.org/bfa/awards#communityI'm making a list of communities that rank well in each state and narrowing down by exploring other attributes.
With all of this said, one of our most favorite places we have visited so far was Fort Collins, CO. We stayed here for three days during a Denver/Boulder/Fort Collins trip. The biking culture in that town is absolutely amazing. It has been awarded a Platinum level by the League of American Bicyclists. I also found it to be a very walkable town. People seemed friendly and generally happy. The size of Fort Collins is just about perfect for us. Cost of living is moderate depending on who you ask, but homes seem to be getting pricier. Weather can be cold in winter with snow, but the area also seems to get lots of sunny days. I had someone from Boulder tell me that they could be in a T-shirt one day in December and then bundled up the next day. As a result, weather may not be ideal for the OP. I can tell you that we were there in the Fall and the weather was gorgeous.
Asheville, NC was another appealing town. Very walkable, great culture, friendly. However, biking culture doesn't seem to be a priority there right now. New Belgium Brewing opened a brewery there a couple of years ago and they seem to be making an impact by bringing the Fort Collins bike culture with them. I'm keeping an eye on it.
We have visited friends in Dallas, TX. We explored other nearby places while we were there, as Dallas itself is too large and traffic ridden for our tastes. The biking culture seemed pretty weak to us. We would like to revisit and head south to check out Austin and other towns just south like San Marcos and New Braunfels, as we see them mentioned often as great places with LCOL. Austin has a Gold rating by the League of American Bicyclists, but COL can be higher than nearby areas.
Some areas in Tennessee, as mentioned by previous posters are on our radar as well.
I'll try to report back as we explore further.