one option for extension is proof of income in the form of monthly payments to your Thai account of 65.000 THB or more. That money doesn't need to sit in the account and can be used as they are coming.
Start coming on 60 d visa extemption or a non o retirement. Start transferring 65k THB per month to a Thai account in your name. That 65*12 is used for extension next year. You can spend all of that if you want.
wrong , you can carry whatever you want but you need a export and import declaration for some amounts. For in Thailand that is over 20.000 USD or equivalent in other currency. Check your country of departure for limits on exports.