If you’ve been depositing ฿65K for a year and also had ฿800K in the Thai bank, can you simply continue with both and then choose a month to switch to the monthly deposits (with the ฿800K kept in the bank), allowing you to choose the yearly renewal month?
I think you’ll need 800,000 kept in a Thai bank. The other option, I’m not positive, but I think you’ll need 65,000 deposited monthly for a year and can then withdraw whatever you want so long as you maintain the monthly deposits. I won’t feel bad if someone wants to correct me if I’m wrong.
If you overstayed 30 days you’re going to have to pay a fine for those days and be ready to leave the country immediately.  you will then have to apply for a new visa at a Thai Consulate which will probably take you a few days or a week.  Be totally RESPECTFUL towards any of the authorities and don’t argue with them about anything they say. Just agree to do it. It wouldn’t hurt to dress a little more formally than wearing shorts and flip-flops, and for God’s sake bathe and wash your hair before you show up.