Troll like Simon should be perma-banned from this group. There are so many threads already and he's polluting with his idiotic non-sense while cracking some "death on arrival" joke which further proves that his post was a troll.
If it's a volunteer visa from an agent, you cannot leave Thailand on your current volunteer visa. You will get denied entry while attempting to come back. If your visa was done without an agent, you can leave and come back without any problem.
I don't know about that, never had an ed visa, but this is what agent are for. If it's difficult to do something while in Thailand or you don't meet a specific criteria, sometimes agent can help you. Ofc it's tea money and everyone get their cut.
You do not need 400k baht with agent, that's the whole point of using an agent. Do not use an agent if you have the 400k baht, they will charge you agent price like 35k baht which should cost a fraction of it.