For your first year you will need the 800k in a Thai bank account. Not all immigration offices allow the combination method. Only the immigration office you use will be able to tell you this
He's wrong. I've always done 90-day reporting by mail, and I'm in and out of the country on a very regular basis. That's in Bangkok, I'm not aware of other immigration offices. Perhaps you're confused
I was on OA with second "free" year twice in a row. I lived in Thailand for four consecutive years. Never once visited an immigration office, never filed a TM30 or a 90-day report. Never got fined.
Get a DTV if you're going to be in and out, the most convenient visa for regular travellers. Keep in mind owning a condo makes no difference, and only switch passports if you're also undergoing plastic surgery to change your facial biometrics, and also get your fingerprints altered