i would contact thai embassy/consulate in your country actually, as they will know more about the laws of both your country and thailand for your situation. this is what i have done for another country in the past
vietnam as home base is likely the best ratio of ease & value for dollar. connection easily to all the countries listed is also affordable(ish) and possible from vietnam. i'm here right now and while my heart stays in thailand, if i wanted to choose a home base out of ease & value, vietnam would be my go-to for sure