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.