Gravel, sand, color... this doesn't really matter and is up to your personal preferences. Depending on how much time you'd like to put into tank cleanings, adding live plants would make it so you don't need to change the water as much but it does require a little extra care on the plant's part and proper lighting and nutrient. If you are leaning towards live plants, you can actually use dirt as your substrate capped with sand. There are many people who have nano NPTs.
I would watch the classified section of the forum for fish up for adoption. However, it's less likely that you will be able to find someone near you. I purchased all three of my newest fish from a breeder and they were shipped to me from TX to NE and they all arrived fine. However, shipping costs aren't cheap, even if someone is willing to give you a free fish, they might not pay for shipping and the packaging needed for it. If you are looking for something cost-efficient, I'd purchase a fish from the pet store. If you don't care as much about price or are looking for a very healthy, vibrant, or "different" fish, the classified forum or private breeders is the way to go.
I don't know if there are any private breeders in TN on here.