It is my understanding that you are not able to use the monthly income method under a marriage visa. as a retired visa recipient I can transfer $65,000 baht a month from overseas and do not have to keep $800,000 baht in the bank. since I'm going to use about that much a month for expenses anyway to me this is better than having a dead 800,000 in a bank account. You are not allowed to have that $800,000 restricted in any way which limits you to non-interest bearing accounts. Good luck!
You're going to have more of an issue finding schools that will process the education visa than the government approving various schools. go on Google maps, search the area that you are interested in for language schools and begin calling or looking at their websites to find out if they will do the paperwork
have you been entering and exiting the country on a regular basis? What you were talking about sounds like a standard visa run which I have done a few times and then applied for long-term visa. these things are stressful, good luck!
if you read through the DTV requirements the only place that you can get your renewal is in person in Bangkok at the 6-month point. You could also do a border run, but I get tired those.