it's pretty obvious they had the bulk of funds for a long period before they topped up to reach 500K. It's not as if there was 2,000 baht in there and topped up to 500k.
Yes for the METV you need to show proof of need, so a ticket out of the country within the time you'd originally be stamped in for (60 days) and then a ticket back sometime after that.
it is not true you have 90 days to make your first entry, he can enter anytime within the 5 years. Although it's typical that you don't apply more than 3 months from your intended entry date.
What consulate? The application has a field for intended/proposed entry date and flight, but tickets aren't demanded unless the consulate specifically asks for tickets.