You can get a re-entry permit but it's only going to be valid until the end of your 90 days. You need to be back before that ends so you can apply for the 1-year extension.
Your entry stamp will be for 180 days. One time each entry you are allowed to apply for a 180 day extension, but pretend that option doesn't exist and just expect to leave every 180 days and return. Many immigration offices do not want you to extend and will make it all but impossible.
it's an entry requirement for Thailand which means if the airline flies someone to Thailand who is denied entry for failing to meet those requirements, the airline can end up being forced to fly that person out at their own cost.
The same reason airlines check for visas, travel authorizations, vaccine requirements etc.
You will receive a 60 day visa exempt stamp if you arrive without a visa. This is eligible for a single 30-day extension.
One requirement to enter as a tourist is proof of onward travel, which is a ticket out of Thailand within the number of days you will be stamped in for (60).
Immigration almost never asks for this, only if you have a history of trying to stay in Thailand for a long time without a long-term visa.
Airlines much more often ask for this proof, and many will not let you check-in for your flight without showing proof of a ticket out of Thailand. Will they accept a bus ticket? That's up to the airline. Every airline sets their own policy. Immigration would accept it.
Have you received a warning before? You're around 5 months in the last year, so it's a little iffy. But generally you will receive a warning before being outright denied entry.
I would recommend having the 3 proofs if you want to enter.
1) Proof of funds (20,000 baht or equivalent in another major currency) IN CASH ONLY
2) Proof of onward travel (a ticket out of Thailand within 60 days of arrival)
3) Proof of lodging (at least the first 1-2 weeks of a hotel booking)
The current situation is that you will not be required to prove ongoing access to the 500,000 baht if you leave and return at least once every 180 days. The situation could change in the future if they decide to check upon entry to Thailand, but it is not likely to cause a problem in the short-term.
To do a 90 day report by mail in Bangkok you need to postmark the envelope 14 days before the due date, and include a stamped self addressed envelope to get the receipt mailed back
Include the following in the packet:
Filled out TM47
previous 90 day report receipt
copies of
data page of your passport
visa/extension
most recent entry stamp
(They used to require TM6, but might be good to include a copy of your TDAC if you have it)