Pages - how to hide header but not footer on first page of section?
Welcome to Ask Different!

Sorry that I don't know the proper solution to your problem through Pages or any other word processor. If you can not find such a solution and still want to do this, you would maybe like to consider doing something similar through a text box in Pages as follows:


Hide the Headers &amp; Footers on the first page again, 
Place a text box via Insert > Text Box menu option and write 1 in it. You can resize the text box by click-and-holding and then dragging one of the selection handles in its edges with a mouse, 
Place the text box at the same location where the page number would reside in the first page, 
Format the text box by selecting the None option in the Arrange > Stay on Page > Text Wrap dropbox menu on the sidebar after clicking on the Format button in the Pages toolbar at the top right. This will make sure the text box remains in the first page and at the same location in the first page even if you add more content to your document,
You can fine-tune the box's location by selecting it and then changing the numbers in  the Position X-Y options in the Format > Arrange tab on the sidebar again.


Hope this helps.