Not true. There’s a lot of nonsense posted on here about using agents - usually by people that have never used them and don’t know what they’re talking about. I’m not recommending anyone use an agent but at least as far as Retirement Visas are concerned there are no issues if you use a reliable agent.
Sorry, that’s not true. I know several people that used an agent for the initial conversion to Non O and first Extension then did each subsequent extension themselves. No issues at all.
RTE London are pretty good and can be flexible. If you are both applying for your own visas then you will both need to meet the individual requirements though.
You can both try submitting the same joint bank account statements and they might accept them. If you already have a pension then you can use that as proof of funds but your wife can show 3 months of least £10k in the bank.
I showed a travel insurance policy when I applied for the Non O. You only need 90 days of coverage. You won’t need Health Insurance for annual Extensions.
You can try applying without a return flight and if they insist just buy a cheap flight out of Thailand within the time frame, or one you can cancel.
You can show a hotel booking for a few days or so as proof of invite/address.
You didn’t say what visa she entered on? If it was a Tourist Visa then around 28k for an agent is correct. It will be to convert the Tourist Visa to a Non O and to do the first 12-month extension at the same time, so your friend will be ok for 15 months.
Unless she wants to mess around and leave the country then she needs to use an agent just this time. If she transfers the money over now, and keeps the required amount for the next 15 months, then she can do the next Extension herself if she prefers.