thats not true for a 90 day non O over 50 retirement visa. You have to be in your own country to apply for a Non OA retirement visa which is a different visa
you should have cash from any country doesn't have to be in baht. Very rare they ask but they would not accept a bank card, visa card or what you have in the bank. Has to be cash equivalent
arh not a good idea, you should have seen what the agent was submitting for you so you know it was all ok. That will be your problem the paperwork will be incorrect
Suggest you each apply for a Non O over 50 retirement visa in Qatar through the e visa online system then when you arrive in hua hin you can open a bank account which will then allow you to each deposit 800k baht and look forward to getting your first year extension
You haven't given enough information to really help other than to guess? If you applied for a soft power DTV then the key is making sure the facility you are using for example if using muay thai then the gym needs to be accredited and the course to last 6 months. The rest of the paperwork is straight forward.