dta's are treaties. You are a tax resident if the country you reside in for more than 180 days DTA's govern what is taxable income and any tax statements between 2 countries. USA taxes works wise income of its citizens, do the DTA with Thailand governs what each country can tax of the others citizens. Let's just age to disagree. That's how it's worked in each country I've been an expat in.
not true. First bite comes from country of tax residency regardless of source of income. For a USA citizen who is in Thailand for 180+ in a calendar year, Thai tax comes first and becomes a USA tax credit.
I had the same issue and entered in 60 day exemption. After I secured housing (couple of weeks) I did a border run to activate the non-o (got evisa in email 2 days after arrival). None of the entry info is on the Evisa. Relax and take your time. It actually gives you more time to get things together rather than feeling rushed to get things done in 30 days
You would in general apply from the country you are residing in. Depending on the country you're going to, you might have to get separate visas if your passorts are different nationalities. If you are married, might be best for her to apply with you as spouse.
You will need a bill of sale (witnessed), signed copies of your and sellers Id/passport bio data, certificate of residency from immigration. You will need to take the vehicle to Pranburi DLT if the vehicle is already registered in Prachuap Kiri Khan province. If another province You'll have to take the vehicle to Prachuap Kiri Khan city. Will cost you about ฿1k. A bit more if you need provincial plates.
Always best to take seller with you too DLT in case any issues arise.