It's your responsibility to get everything done fast enough to get the money in your bank account so it's there for 2 months already in time for you to apply for your extension.
If you do not get your 800k moved into your Thai bank account in time, you have no options. You must leave Thailand and start over with a new non-O visa.
I guess technically you have the option of using an agent, but that would be a lot of money for something you can do yourself by leaving and getting a new non-O visa.
Most immigration offices only need a TM30 to request a certificate of residence. So you should have been able to get that within days of arriving in Thailand.
Then after you leave, apply for a non-O visa from a Thai embassy through the e-visa system. Then when you arrive in Thailand you are guaranteed to not have any issues and you'll be ready to apply for your extension after 1-2 months.
The only way your plan works is if you ALREADY have a Thai bank account. And even if you do, it's going to require AT LEAST 2 extra trips to immigration which is not a pleasant thing for most people.
A 90 day report is simply you reporting that you've been in Thailand for 90 consecutive day. If you're not in Thailand, then you haven't been in Thailand for 90 consecutive days. You start counting again from day 1 when you return, but you won't be able to do it online then. You'll have to go in person as the first report after entering Thailand must always be in person.
STOP spreading misinformation. This is ONLY for Laos. You pay online everywhere else. In Vietnam you pay online. In Cambodia you pay online. In Malaysia you pay online. It's only Laos.
Technically no, if there is no stamp in your passport with a consideration date, then your permission to stay ends on the date in your passport as normal, because there is nothing in your passport giving you additional time. I would probably go back to Krabi on your last day if you cannot get ahold of them.