take a train
as soon as they build the tracks and offer service, that would be a good idea......CM to UT, not BKK.
won't comment on the rest, but if taking bus, try VIP/407, (ac, 24 seater, almost comfortabe, faster) as gov't busses, hopefully better and safer, and no price scamming or thefts. if no vip/407 service, i would consider flying, if not driving yourself. as mentioned, it is a pleasant drive, i've done it a couple times, enjoyed it.