Do I need to cancel my ED visa before leaving Thailand if I have a new passport?

I would like to know whether it's necessary to cancel my ED visa before I leave Thailand. My current ED visa extension expires in December. I have to leave Thailand urgently, early next week, and will probably not be back until next year, after the extension has expired. I may only be coming back to pick up things in storage before leaving again, or I may want to enter on another non-immigrant visa, I'm not sure yet.

A complicating factor is that I'm picking up a new passport on Monday, which will have a new passport number.

Q1. Is it necessary to cancel the ED visa even if it has already expired by the time I come back?

Q2. If the answer to Q1 is normally yes, is it still necessary to cancel the ED visa even though I will be returning with a different passport?

Q3. Assuming it is necessary to cancel, my school said they can just supply a letter of cancellation. Does that letter allow me to enter Thailand on a different visa, or on an exemption, without going to immigration to cancel the ED visa first? Or is it absolutely necessary to cancel the visa before I leave? I have very limited time before I leave which is why I'd like to avoid going to immigration if possible.

Q4. Do I need to go to immigration anyway to get the last entry stamp transferred to the new passport? Or can I exit by showing the entry stamp in my old passport?

Q5. If I cancel the visa before I leave, how long do they allow me to stay in the country after the visa is cancelled?

Q6. My wife has a non-O dependant visa based on my ED visa. Is it necessary to cancel that as well, or only the ED visa?

Thanks for any assistance, this situation is too complicated for me to figure out from previous posts.