on the Thai e-visa website in your home country apply for the type O 90 day visa based on retirement. Because you are both over 50 you will both need the equivalent of bt800,000 in each of your bank accounts, and yes thinking long term you will both need separate accounts. Not all embassies accept joint accounts. Once in Thailand for convenience you will both want separate bank accounts for your everyday shopping needs, as you can not have two debit cards on the same account. You each need a long term visa to open an account here. Once you are here on your type O 90 day visas you both open Thai bank accounts, and transfer by SWIFT transfer the bt800,000+ into each account, as you need these Thai accounts and money to get your one year extensions as soon as the bt800,000 has been in the Thai accounts for at least two months. It is all pretty straightforward, and the easiest visa, and yearly extension to get. This is how it is done now, because of changes preventing anyone on a tourist entry from getting a Thai bank account. The type O 90 day visa you will get is good for 90 days to enter Thailand, and stamped in for 90 days when you enter. As it gets closer to when you want to come here I can give you more up to date at that time details.
Do you currently, or in your past, ever had a business, not working for someone else, and payed appropriate business taxes? Thailand is not a training ground. The BOI expects experience, and professionalism. Most that use the BOI do it by setting up a branch office here of their existing business in their home country.
crypto trading is taxable in Thailand. This went into effect two years ago. Untaxed money coming into Thailand is a big no no, and considered money laundering if you don't pay income tax on it anywhere.
consider the fact that you can not pay a hospital bill in Thailand with crypto. Because of that fact the bt800,000 has to be in a bank account in your name only that could be used to directly pay a hospital bill. That is the reasoning about what kind of account is legal to use.