Each embassy has their own rules and requirements. You check the embassy website that you will be using to apply because any other embassy's rules don't matter
you check the EMBASSY website, not the e-visa website. The embassy is the one who will receive your evisa application actually process it. It's what they require that matters.
You don't have an education visa. You have an education extension. You are indeed required to cancel this at immigration. You need to get a letter from your school that states your final day of study and then take this to immigration. You can go about a week before the date on the letter at most immigration offices and then they will cancel your extension and stamp you in until that date.
Reports from a few embassies in SE Asia that they require the printed statements but they'll also require you to open your banking app when you're at the counter submitting your application to show the live amount in your account
A 90-day report is for reporting when you are in Thailand for 90 consecutive days. If you leave Thailand you are not in Thailand for 90 consecutive days. When you return you start counting over again because it's only for consecutive days inside Thailand.
Every province has an immigration office. But the requirements at each office can be different. Here is a list of common requirements but as I said it will vary.
Most offices allow you to apply for an extension when you have 30 days or less left on your existing stay.