It's either $30,000 as a lump sum OR $2,500 a month. Not both.
I'd go with the monthly income, get a bank account when you hit the ground in Thailand, and start transfer at least the minimum monthly required for the extension.
You'll have plenty of time to get that sorted with the Non-OA visa, but it doesn't hurt to start early.
They are mostly targeting accounts that have been opened on tourist visas using shady agents, as far as I understand it. In a effort to combat money laundering or something.
If opened yours legitimately, and then you change to a DTV it SHOULD be fine. And if it isn't, it should be fixable by verifying yourself at a bank branch. Probably the one where you opened the account in the first place.