Much easier to get non-o in your home country before you arrive. In London only took few days. I tried the same as your plans but instead returned, organised the non-o and went back to Thailand.
Non-OA requires health insurance and can be obtained only from home country. I am also collecting for 2nd renewal: Samut Prakan requires verified (stamped) TM30, as i am moving onto 65,000 monthly transfer method i am awaiting the 12th on 4th of August. Proof that I maintained 800,000 for 3 months from the last extension and minimum 400,000 thereafter until the 2nd extension application. I will also prepare schedule of transfers from Wise to my BKK a/c which seems to be the recent requirement in some IOs in addition to transfers being shown as “Foreign Transfer”. The form, 2 copies of passport including visa pages, photos and 1900 baht. A checklist for both of us. Anything else to add?
I was watching the person in front of me sailing through in seconds, no questions asked - on DTV visa. It took me much longer especially to check in with the airline and go through immigration at Suvarnabhumi airport on a “proper” Non-O visa: still valid and a re-entry permit. But i do believe the scrutiny will increase as we progress through the years of the new DTV visa especially the financials and proof of payments for ongoing work if remote work DTV.
Rent can be 8000 or even less a month for a studio (in BKK’s oversupply market). You have 30,000 left after rent … average salary here is 15,000 per month (info for your own conclussion).
Compliance is low and enforcement non-existent. Thailand taxes only remitted income not (yet) worldwide earned. Most countries would have a double taxation agreement with Thailand which enters the computation ensuring that only up to the highest tax bracket of both jurisdictions is paid and not paid twice. Personally i make sure i do not become a resident for tax purposes nowhere else but the home country.
You can do within Thailand as long as you have at least 2 weeks left on the current tourist visa (exempt / extension) but applying from outside and especially home country is so much easier…. At least as I assesed at the time in my case after enquiring with two IO: Jomtien and Sriracha.