Even if you go to an agent and get a Non-o 3 month + 12 month extension you will still have to open a bank account and put in 65k or 40k baht (depending on visa) minimum (not average) for 12 consecutive months before your next extension and keep doing it
Might get an under consideration stamp with a date to come back. Immigration won’t keep your passport when under consideration just go back on the date they stamp in your passport. They may also do a house visit to see you are actually living where you say.
Yes, come in on 45 day exempt, go to the immigration office in your province in the first week and apply for Non-o visa (you get 3 months), immediately open a Thai bank account and transfer in 800k baht. A month before your 90 day Non-o expires apply for a 1 year extension.