tips about route or anything else that could help?
Are you familiar with the route possibilities already? I've lived in OH, KY, TN and SC and been over these roads quite a bit, including retrieving 4 HMMWVS from NC to KY last year. The most logical route is to get to I-75 in Ohio, then I-75 through KY and TN, then I-40 east.
If you want to avoid hills (and cities), you could consider going around Cincinnati on the west side. There is a big hill entering KY on I-75, and the east side bypass is hillier than the west side. It adds a lot of distance, though, being a really big loop.
http://www.cincinnati-transit.net/I-275.html
There is a big (up) hill at Jellico as you enter TN on I-75. There is a truck lane and there are usually some slow-going trucks. When pulling a trailer, I try to fall in behind a tanker as they are usually heavy and slow. You could also consider taking 25E from Corbin down to Morristown...it's a pretty drive and there is a tunnel. (We used to live in White Pine TN where 25E intersects I-81.)
Once you get to around Newport TN I-40 is curvy but fairly flat as it follows the Pigeon River. You will still want to watch your speed.
When are you planning to make the trip?