I'm not sure about what you said. That is not how I understand it. To keep your visa, you must have THB800,000 in your account 3 months before and 3 months after which means for an annual visa renewal that money stays in your account. I'd be interested in any update on this as it affects me as well.
you have two options: transfer the THB800,000 all at once or any number of amounts. But the full amount must be in your account 3 months before you apply and stay 3 months after. Or, you can put THB65,000 into your account every month for 12 months then apply. You cannot miss say a month then put double in the next month. The authorities won't accept that. They need to see you have a regular monthly income. The authorities were forced to change the rules because of rorting by foreigners. Hope this clears it up for you.
I'd be very careful. In fact I wouldn't trust anyone with my passport. I won't let them take it at a hotel for photocopy the page unless I can watch them.
When transferring money from my bank in Australia I always use Australian dollars. The reason is that one always get a better rate of exchange in a Thai bank. Or you can set up an additional account in Thailand to transfer the dollars into it. Then leave it there until the rate improves; then convert and transfer into your main account.