I checked with our local orb I tor last year through a Thai friend, and long term stays are not an issue, couldn’t get a commitment on the 30 days “rule”
Check on line option, UK allows you to apply for IDP on line and mail to your address in UK and get sent express mail to TH - not sure what country you are from - other option of course is take test here if you are around long enough
Horses for courses, if you take the agent route, very hard to normalize your status. You will be beholden to agent system - there is risk if they screw up or lose your passport, my passport never leaves my sight feel more comfortable with that - earn 20k a year from the money I keep here for visa, might get more in UK but then at the mercy of exch rate when I bring to Thailand…….always the risk that govt cracks down on corruption in immig which the agents feed……
65k a month through WISE to SCB has worked for us - over 15 months now selecting correct reason for transfer is important so it shows funds come from outside Thailand.
travel made easy - no standing around in arrival queues, makes it easy to collect tourist tax as well without impacting residents…..been in place in many countries for a while now takes the aggravation away….love flying to Malaysia, Singapore and Aussie these days.
WISE rates in my experience are always better than anything you can get through most major banks so that probably answers your question, I get my pension paid to my UK bank and then move it when needed give me better control as well. Keeping an account when non resident might be your only challenge.
Go to your local tax office personally, preferably with a Thai speaker if you are unable to do that you would need to get a local tax accountant to assist you.