Best to meet the seller at the Land Transport office to ensure the name change can be done. That was the advice i never took but typically i dont pay much for cars to care.
Stay 6 months in Chiang Mai, Pai, 6 months somewhere else. Or 3, 3, .... Why not explore. I know we're brainwashed to plunk ourselves down for 20 years but that gets boring real quick in retirement.