As david said, non immigrant visa holders don't need to show onward travel. Also, a visa and an extension of stay are 2 different things, and have 2 different sets of requirements.
No, you cannot get a 30 day extension on a 90 day Non-O. You can only apply for a 1 year extension, but it would require you to have 400k baht in a Thai bank account for 60 days before you applied for the extension.
Stop copy and pasting random stuff off the internet. If you want to link an article then copy and paste the web address so people can read the source. Also, try and keep your thoughts to single comments. It starts to look like spam when you post 6 comments in a row and just copy and pasted text, no one is going to read it.
STV is an awful option, I wouldn't recommend it to anyone without a current house in Thailand. You need 90 days of accomodations pre-booked AND health insurance for the duration of the stay, including each 90 day extension.
If you aren't planning on staying more than a year, you could take the money out right after you get the yearly extension. You just wouldn't be able to extended it next year, you'd have to start the process over by getting a new Non-O if you wanted to stay another year.
The Non-OA doesn't have that requirement, you just have to show that you have the equivalent amount in your home country's bank account when you apply. The biggest downside to the Non-OA is the health insurance requirement.
Paul, there's 2 types of retirement visas, Non-O and Non-OA.
The Non-O can be gotten outside of Thailand or inside thailand and is 90 days, but you can extend it inside the country for 1 year, however you need 800,000 baht in a thai bank account for 60 days before you apply for that extension. There is no background check or health insurance required for it (besides the current covid entry requirements).
Then Non-OA is a 1 year visa that you can ONLY apply for in your home country. You cannot apply for it in thailand. The Non-OA does not require money in a Thai bank account, but is does require specific health insurance.