Simply don't put in a Thai bank account. Your home bank account is ok

For Insurance it depends on what you are calling a retirement visa but im guessing as you appear to have obtained it via an agent (as that's the only way you get 15 months) that you actually have had a 90 day Non-O visa followed by a 12 month extension of stay. An extension based on a Non-O visa has no insurance requirement. When you got the initial non-o visa did you show 800k baht in a bank account in your name, and similarly for the 12 month extension? If you didn't you will be stuck using an agent again, you won't be able to do it yourself

You just show both passports on the way out. You have nothing to transfer. But be aware that having a new passport does not hide your history of living inside Thailand so you may have an issue when you return

It seems strange to ask the same question in a different forum and expect a different answer. The answer is the same. It will depend on the immigration officer you will stand in front of on the day

Immigration office dependent, go and ask your local office

Anonymous participant i really don't know but I'd be very surprised if VFS were making the decision although they may be doing the initial sift. My only experience of VFS is here in Thailand when renewing my passport, they check the forms & photos are correct and then just send it on to the UK for processing

Anonymous participant no embassy will do that any longer unless they call you in for interview (which is normally just a formality).

When I renewed mine earlier this year I went to immigration and got the stamps moved shortly after. I had to do the next 90 day report in person so I would do it at the same time. I didn't update the bank until 3 months later when I went to request statements for my annual extension, wasn't an issue.

You would need to write yourself a contract with the company that gave you permission to work remotely from Thailand and charge through the company. You sure seem to have gone about this in the hardest way possible, why not just be a freelancer? Show your contracts with the companies you work for, show income, show the 500k and you should be good to go. The alternative is Soft Power but they can still ask for evidence of how you will support yourself for the 5 year period of the visa

You can switch from a DTV to another visa type inside Thailand at an immigration office, but I don't think its possible to do so outside Thailand