Kuala Lumpur is 24 hours but you have to have insurance, police check from your own country and a medical in KL. Phnom Penh had fewer requirements in May, but they take a week.
You definitely want a car on Samui, taxis are extortionate. If you're thinking of buying a car/bike, you will need to buy 'certificate of residence' from immigration. Also need one for your driving licence. Probably easier in your wife's name. If you want a 4x4, buy a car in Bangkok and drive it or get it shipped. We live on mainland opposite Samui and I spent a while waiting for a few year old 4x4, ended up buying new, everything was in Bangkok, nothing down here. First class insurance on a 1 year old Mitsubishi Pajero 4x4 is around 20,000 baht a year.
We've just been to Cambodia (Phnom Penh) and Malaysia (KL), they no longer issue Non O Dependant for anything but Non B visas. We applied at both, denied at both and advised the same about Non B. Nothing to do with having initial 90 days or 1 year extension on main visa.
I spoke to Consular officer at Phnom Penh (not the people at the windows), she confirmed they did issue it previously but now cannot.
Unless it's changed from 3 days ago, I had to submit insurance and it still says Insurance Required which you have to tick to confirm. The Thaipass shows country of departure, arrival date, valid until. Now, I also applied end of May and that had a 7 day grace from arrival date. The one I applied 3 days ago (we changed country of departure) only has 3 days grace. The problem you may have without Covid insurance is the airlines are scrutinising the documents (before departure) that you need to get the Thaipass. Presumably because they'll have to fly you back.