Immigration will very rarely ask for an onward ticket out of Thailand. They could. But it’s rare that they would. If you have had an extensive history of previous entries then they could ask as a method of denying you entry. A typical tourist would never be asked.
Assuming you’re from a visa exempt country you don’t get a visa on arrival. You get a free entry stamp for 60 days. You can extend that once for 30 days at a local immigration office.
You can leave and return for another 60 days stamp and another extension if you want.
How many times you can do this is unknown. You may get away with 2,3 or 10.
Entry in to Thailand is at the discretion of the immigration officer you hand your passport to. No one can tell you whether they’ll accept your entry or not.
They want to see 500k baht equivalent in a local bank account. That’s for the application. We don’t yet know if they’ll need to see anything like that for an extension.
That’s subjective. On the face of it it seems to be. You won’t want to be getting an extension as it’s 10,000 baht but by bouncing you can get a 5 year stay.
The offset is that you can’t work for a Thai company in Thailand on the DTV, but you can on a marriage visa/extension.
You are correct. The MFA sell the visas. Immigration set the policy for extensions. We have been reliably informed that the extension cost is 10,000 baht.
Obviously no one is nearly close to needing one so it remains to be seen if things will change in the mean time.