OK, now it seems to work (more or less, because on the first page I still don't need the number of total pages in the footer)
Another problem:
Your code for Section 2 looks like this:
{={PAGE}+{Section 1}+{Section 2}}
I'm trying to add Section 3 to continue numbering but it returns a syntactical error for this code:
{={PAGE}+{Section 1}+{Section 2}+{Section 3}}
What do I do wrong?