Haha! The only way to get off the agent merry go round is to leave the country and start again doing it legitimately. You're going to have to be paying the money to the agent every year from now on.
I tried it once but CW wouldn't wear it. They want the proper print out from the bank. I guess in the country renowned for "fakeness" they are well aware PDFs can be edited
There's no official limit. Purely at the discretion of the immigration officer when you enter. Expect to be denied on your third attempt. As soon as they work out you're abusing the visa exempt concession, you're done, with a black mark on your immigration record. There's a reason Thailand has a variety of visas allowing longer stays