I bought a new car in Bangkok in 2022. The only deposit was 10,000 baht to secure my name on the list of customers waiting for a car to become available. At that time I waited 4 months. Once the car arrived I just transferred the full price using my banking app. I was on an OA visa and I needed a residency certificate and my passport. I think that was all there was to it. A year later I moved to Sisaket province.
As long as you are here on the proper visa then I wouldn’t think you should have any problem switching from one visa to another. Sometimes people staying in Thailand on educational visas as students have future problems but it sounds like you are pursuing a work visa at a university.
If he is in the very first year of the OA visa then he cannot cancel it. He has to wait until that first year runs out. The original visa has to expire. After that you have options.
Unless it is one of a kind or has sentimental value I wouldn’t ship anything. Anything for day-to-day living you should replace in Thailand. Six years after moving here I shipped some artwork made by my father who died 20 years ago. The shipping was expensive but it has sentimental value.
I lived in Phra Khanong, Bangkok for 6 years and did not need a car. I used the BTS/MRT, taxis, motorbike taxis, and Grab. Occasionally we rented a car for excursions. We moved to Sisaket province in 2023. There is no public transportation out here. I bought a Honda CRV. I loved not having a car in BKK but I really love the freedom of having a car now that I am outside of BKK. I’ve got a motorbike here in the countryside for short excursions. Motorbike accidents are common everywhere in Thailand. My wife’s daughter got in an accident a couple of weeks ago. I see accidents pretty regularly.