@Bertie ********
As a resident of Dubai and being over 50 years old, you will be able to apply for the 90-days Non-Imm-O retirement visa by the E-Visa online system with the Royal Thai Embassy Dubai as the processing Thai authority.
*** you need a financial proof, you said you would be able to show a minimum of equivalent 800,000 THB in your bank account in Dubai.
So YES, you would fulfill the financial requirement for the application to the initial 90-days Non-O Visa
*** when you enter Thailand on this visa, you will get stamped in for a 90-days stay permit.
As soon as you can, get your accommodation TM30 registration, visit Immigration and ask them for the “certificate of residence”. Get a Thai mobile phone number.
Then open a Thai bank account either by yourself, or let an agent help you with this service. It should not cost much more than 5000-7000 THB.
***using an agent saves you from running around trying to open a bank account by yourself – some branches will still give you problems, even on a Non-Imm-O visa, and some will try to sell you unnecessary insurances as a side product.
***you can apply for the “1-year Extension of the Stay Permit based on Retirement” (which some people wrongly call “retirement visa”) on Immigration, as soon as the 800,000 THB have seasoned in your Thai bank account for 2 months, and you can show the “bank letter of guarantee” which confirms this.
***it all is doable within the 90-days stay permit an entry on a Non-Imm-O Visa will grant you. All you need is getting your ducks in a row and get things done properly. Every Immigration has slightly different rules on the requirements to an application for the “one-year Extension”, so you should pick up their list of requirements in their office in the first week after arrival.
***alternatively use an agency for peace of mind, for the service of opening the Thai bank account and taking care of your Extension application
Good Luck and a good time in Thailand