from reading across multiple platforms of people's success and unsuccessful DTV applications, a lot of embassies are requesting to see tax returns. So of you don't want delays it's better to just include it in your submission.
an ED visa isnt a tourist visa and its very easy to open an account on an ED visa, youre comparing apples to oranges. The vast majority of people opening banks on tourist visas are having to use an agent because of banking regulation changes over the last few years. The vast majority of banks will outright refuse anyone on a tourist visa or its equivalent, sure you probably can find a bank that will accept it, but it's going to take you days on end and probably more money than paying an agent as the ones that do, will likely require you to purchase insurance.
We if you leave without a re-entry permit you won't have a valid extension anymore.
I hope you are actually learning Thai too because on re-entry you are going to get questioned in Thai and only Thai and if you cannot answer they will deny your entry.
Assuming the kids are still young, they just go on the back of your wife's DTV as dependants (your wife submits an application for the DTV, once accepted you can apply for dependant DTV visa, if they will be going to school here you also have the option of Education Visas for them which the school would sort out for you.
depends on the office, and even the IO you see. Some will want it some won't. Better to have it with you, just ask for a copy or for a file to be sent to you on Line or another messaging service.
TM.30 is filed by the hotel, agent or landlord of where you're staying. If you're renting a condo or Airbnb talk to the owner first, even if you've already booked and they won't file one for whatever reason, you can get aroind this by staying in a hotel for a couple of night and get them to do it.