You can take NH-8 all the way a bit beyond Bawal and short of Dharuhera where you need to get on to NH71 for Jhajjar -> Rohtak -> Panipat. At Panipat, join NH-1 and drive towards Karnal. Roads are great.
Between Behror and Neemrana, you have Hotel Highway King and Sagar Ratna on your left, where you can have lunch/snacks. Can't comment on hotels/dhabas on NH71 though.
While you are in Karnal, take time out to eat at Puran Singh in Ambala.. finger licking, smacking food! Slurp Slurp