Yes, you are subjekt to tax after 180 days in Thailand, but funds you’ve already earned, taxed and saved in a bank at home is not subjekt to tax because they are transferred to Thailand for extension as income for the first year would be.
Unless your embassy offers to provide you a affidavit letter to confirm your income, there’s no legal way around banking 800K in a Thai bank account for your first one year stay in Thailand.
For the initial 90 days Non O visa you can use your bank account at home.
Regarding funds, you don’t need to leave any funds in your accounts after the extension is issued as for based on retirement, just bring your account back in 400K two months prior to your next application. You bring a receipt of your TM.30, copy of lease contract is normally ok, some immigrations require copy of housebook and owners Id card as well.
Yes, the problem is anyway that you won’t get any extension of any of these visas in Thailand without proving 800K baht in a Thai bank for the first year.
If you plan to move to Thailand the best option is to apply for a regular 90 days Non O visa which don’t require any police check up. And if you don’t have a permanent registered residence in the Philippines at date you can’t apply for a Non O-A visa anyway, which in fact requires a further police check up, a mandatory Thai health insurance and a medical certificate.