Daniel Boone NF/Cave Run Lake area in KY is really nice. It's an hour at the most east of Lexington, right off of 64. Cool little BBQ place there called the Pig Out BBQ, on 801. It's between 64 and Cave Run Lake. It's just south of where HWY 60 crosses 801, on the left hand side. How would a boy from northern Indiana know how to give directions to a BBQ place in Morehead, KY? It's good food. Also if you overnight there, the Comfort Inn at 64 and 801 is a decent place.
Knoxville to Lexington on 75 is a nice ride, but I would stay on 75 all the way to Cincy, then hit the 275 bypass, then take 74 to Indy. It's a quicker than going all the way to Louisville and then north.
Depending on how tight your schedule is, you may want to consider staying on 64 through Louisville all the way to 231, and then take the 2 lane north. I've never ridden this route south of the Crane Naval Depot, but north of there it is a nice ride all the way north. When it gets up to West Lafayette, it changes to 421, however, and flat farmland from there to the state line.