We did this. Get a letter from your school saying your course is finished. Go to Thai immigration and have your latest extension cancelled. They will give you a new stamp with a new exit date. We got one week from the cancellation date. Later, we got out DTV in Vietnam no problem.
I have three bank accounts and showed all three for a combined total of 500,000 baht. it wasn't a problem for them. I had no ticket out of Thailand and they didn't ask for one.
I took advice of others and had a very precise cover letter listing all the documents I was giving and especially showing how the bank accounts added up to the final total of more than 500,000 baht. I think that helps a lot as they don't have to figure things out on their own
I applied in Ho Chi Minh and did not show any contracts. However, I showed my portfolio and resumé. I stated in my cover letter I was applying as a freelancer. IMHO, it all depends how you present yourself
no proof. they asked for current address and I put our hotel in HCMC. they ask for proposed address and I put our condo in Bangkok. they ask for permanent address and I put where I get my mail in Canada