Current water temp is 74. You can check it daily on the front page of this website:
www.lakecumberland.com. This is the best time of year on the lake in my opinion.
If I were you I would check into renting one of the "boatels" at State Dock. They are houseboats that you just rent but just dont leave the dock. Its cheaper that way and if you have a few in your group, it can be cheaper than a hotel room. I think you have to call and ask, its not mentioned on the website.
If you have room for another rider send me a message