Middle Tennessee is wonderful. I moved back to Tennessee after living in Sarasota, FL for the past 6 years and I wish I had not waited so long. I grew up in Franklin County, TN in a town called Estill Springs. It is on Tims Ford Lake and is a great area. From there you are an hour from Nashville, an hour from Huntsville, AL and an hour from Chattanooga. There are mountains, valleys, huge lakes and flat farmland. Great hunting and fishing and land is still reasonable.
I live in Clarksville, TN now because of work. I lived here in Clarksville about 12 years ago when I was in the Army and it has grown alot.
The counties you mention are not bad. Grundy county would not be a good choice. Very poor area, lots of crime and meth use. Winchester, Tullahoma, Shelbyville, Manchester are all good choices. They are small towns with little more than a movie theater, bowling alley and a few eateries. Tullahoma has a mall and a few common chain restaurants. The closer you get to Nashville, the more you will pay. Checkout Hillsboro, just outside Manchester. Land is cheaper there.
While you are looking, check out a few towns west of Nashville. Dickson, McEwen and the I-40 towns west of Nashville. North of Nashville can be expensive if you go up I-65. However, if you go up i-24 towards Clarksville, then Springfield, Joelton and that area is still pretty nice.
Feel free to PM me for any info you need. BTW, I was born in Alabama and still have most of my family there. It would take a lot for me to go back to Alabama. Tennessee continues to grow while Alabama continues to struggle. FWIW, Tennessee is the 2nd best state to start a new business. Tennessee offers new companies a nice incentive package and that is why they are getting so much new industry.