for burmese if they ask for proof of funds they have typically only asked 10K baht because they can only get in for 14 days BUT you're right, having 20k in cash would be better 🙂 ( i edited the post)
As long as you fly in you can get 14 days exempt when you enter, you can't enter by land as a burma passport holder without a real visa to thailand
You might be questioned comin' back in though as you've been here a LONG time
Depending on how they want to be they can require you have proof of 20K baht in CASH, proof you have onward travel in 14 days and proof you have lodging for the 14 days
doubtful you have ANY Non-b VISA, and it is far more likely you have an "extension of stay" based on employment here (LOOK at the stamp in your passport)
No problem at all applying for a DTV on a current extension (even with a re-entry permit), you just have to make sure when you stamp IN to the country you tell the officer at passport control you want to enter on the new DTV
AND
You need to GO to the immigration office in thailand that issued your Non-B extension and cancel it after you're back (you will probably be fined for not cancelling it when you left the country to get a new visa)
the one year extension is ADDED to the expiration date of the 90 day stamp from the Non-O <- which means with the Non-O and the year extension you have 15 months total 🙂 and each year after that will be added to that same expiration date year after year
This is a general list of things required to get a 30 day extension on a 60 day visa exempt or 60 day tourist visa entry stamp. Remember there are over 80 offices in the country so what yours requires might be a bit different
More and more offices are requiring that you have a TM30 receipt (showing you're registered as staying in the area served by the immigration office)