Once you get out of Bangkok it is quite an easy drive if you are a competent driver, it is dual carriageway all the way. Watch out for the orange (roadworks) signs as they often give very little notice of roadworks.
It is a long drive to do in one day, I have done it a few times from Hua Hin, but that is 3 hours less than Bangkok.
The statistics are high for road deaths here, but I suspect that is because of the number of deaths at night time on scooters when under the influence of alcohol (Thai and Foreigners), so avoid driving past about 6pm if you can. Good luck.