Mac Mail Mailbox Rebuild and Attachment Download Setting

I have several questions regarding the Mac Mail Mailbox Rebuild operation and the Mac Mail Download Attachments Setting.

My MacBook Air is regularly running into a problem syncing photos due to a "Not Enough Local Storage" error. I am looking to provide more local storage.

Compared to my iPhone and iPad, I saw that Mac Mail is taking up a lot of space. On the Mac, Mail takes up ~16GB and on the other devices it takes up only a few hundred MB. I have put in a suggestion for Apple to have an option to handle Mail on Mac similar to the way it does on my iPhone/iPad. As this "fix" may or may not come, I thought I could try to save space by changing the current Mail Setting that downloads all mail attachments (ALL) to not download any mail attachments (NONE). And then I would rebuild my Mailbox(es). And save some space. And maybe my Photos could sync again.

Questions:

1) When I go to the Rebuild Option in the Mac Mail "Mailbox" menu, do I have to rebuild each "folder" or does it rebuild all the "folders" for my "account"? [I believe in Apple lexicon, "Mailbox" is equivalent to what is regularly referred to as a "folder". So, I believe I will have to rebuild each one separately (after I have selected the option not to download attachments). I just wanted to confirm.]

2) If I set the Mac Mail Setting under Accounts to not download any Attachments, when I look at a particular email that has an attachment, and the attachment is viewed, does that attachment now stay downloaded (like it was when I had it set to download attachments)? (Part B: If yes, does that mean that I will have to periodically Rebuild the Mailboxes to get rid of all these attachments in the mail that I look at if I need to keep space available?)

3) If I set the Mac Mail Setting under Accounts to download only Recent Attachments (which I believe is 15 months worth), as time goes on (say one month / two months), do I end up with 16 months / 17 months worth of downloaded attachments or do the attachments for the oldest month get removed each month?

4) An apple support article I came across seems to indicate that some Mail attachments (photos, pdfs, etc) are downloaded automatically no matter what, and the Download Attachments option applies only to other files like spreadsheets. That same article refers to a popup menu to change this, which does not seem to apply (since it is in Account Settings not a pop-up). Is it correct that the Download Attachments (All/Recent/None) account option only affects a certain subset of attachments? (That may limit my space savings in Rebuilding.)

Thanks in advance for your support.