if you are over 50 it makes sense to get either a Non-O or a Non-OA visa particularly as you own a condo. Personally I'd get the Non-O but the choice is yours
You need to have a job for the LTR option you propose plus meet the other requirements. You can't work in Thailand on a DTV. Seems to me your best option is to find another job that will support a Non-B and Work Permit
correct. He know lives in Thailand, he is just another tourist and can only stay for 180 days at a time, he may well lose his bank account due to being a tourist, he can no longer get a 5 year driving licence etc.
As well as having the 500k baht in the bank it is increasingly asked how you intend to support yourself for the 5 year duration of the visa if applying using soft power. Think carefully how you respond if asked