For a marriage visa you need 400k in a Thai bank account for 2 months, but if you don't already have an account you won't be able to open one on a tourist stamp. If you are already married to a Thai and have documentation to show, leave to a nearby country and apply for a 90 day non-o there, return to Thailand and open an account then transfer the money. As for an METV you normally have to apply for that in your home country
you are applying for the wrong thing, if you will work remotely from Thailand at any point in the 5 years you need to apply for the workation option. You can still do Muay Thai alongside it, but you can't work alongside Muay Thai. The options are quite distinct.
you write a letter from yourself as the business owner to yourself as the visa applicant. May seem strange I know but that letter is a fairly basic requirement. It should give you explicit permission to work remotely from Thailand.
It sounds like you gave way to much information on the tourism aspect and not enough on the work aspect. And best to ignore ChatGPT. For workation you need to emphasise how you can manage the resort remotely, you also need a letter stating you have permission to work remotely from Thailand and of course show financials. So invoices/receipts matched up with bank statements would help, but also that it pays you a regular income which you can show. Also helps if you show you are registered to pay tax and supply tax returns
Was it rejected or cancelled? If it was cancelled it implies an error with your bio data. If it was rejected how long was the course for? Did they ask how you will support yourself and if so how did you answer?
Anonymous participant hardly the purpose of the DTV. You don't qualify for the workation option. I guess you could apply under soft power but they might not give it to you looking at your work schedule