Many of the schools don't care whether you attend or not. However, there is always the risk that the immigration officer will test your Thai. They've tightened things up from when I first arrived. So, if you go the ED route and you really want to stay, you're going to need to attend classes. If you can't afford the classes, you're out of options.
You can update your bankbook on one day. It will show all historical transaction. I did that. But IO also wanted to see a signed printout of formal letter from bank, with bank stamp. I used SCB and had no problems. But, I'm not in CM.