What to wear in Nashville
I think the most important thing is to dress comfortably. You're probably doing to be walking a lot so comfortable shoes are my goto (if it were me, I'd wear the best pair of running tennis shoes "sneakers" you have. One pair of nice jeans for a dinner. However peak of summer you won't find me in long pants no mater what!) Nashville is considered a casual type town. Heck, the richest people here wear cowboy boots and hats! That's a joke, but I'd seriously aim for comfort not to keep up with Joneses.
Even upscale reaissturants have a relaxed dress code. There are some which require a jacket for guys, but not many.
Nashville experiences all four seasons - freezing in the winter and blazing hot in the summer. So just check the latest weather and plan according. And remember, boots may be comfortable, but not required :)