Great program & many thanks.
First question as I try out program:
What determines the file order when Tag Editor is opened
and how can I change the order?
The order is supposed to be by track number (and the files are supposed to be from the same album). Files whose track numbers are missing are put at the end of the list and they are sorted by the file name. Since you're asking this, I guess your files either don't have track numbers or come from Vinyl or tape, where numbering might be different.
One way to change the order is to first assign track numbers manually and then press on the button with an arrow pointing down, called "Sort by track number".
However, I suspect that this isn't what you want, so I guess it would be better to post a list with your files from some folder / album and tell what you want to achieve (i.e. how would you want them sorted and why.)
(Ordering by track number is important when downloading or pasting album info.)