You could — painfully — manage alternate left/right footers by making every single page the start of a New Section and doing a bunch of copying and pasting of footers. It wouldn't handle document flow well, though (it'd have to be a final step that you undid and then redid if you changed the document).
Uneven left/right margins would require a lot of manual effort. You could use a Stay On Page invisible (no fill or border) rectangular shape with an appropriate Text Wrap setting that you manually placed on alternating sides of each page. Because the page numbers would stay odd/even automatically it would handle document flow ok.
All of which is to say that Pages is no longer a decent double-sided document creation tool. Facing pages is one of the many, many things I'd like back from Pages '09, but I suspect it will never, ever return because print is effectively dead from Apple's perspective. iBooks Author is probably their solution, but it's pretty much abandonware at this point and needs a lot of work.
I'm seriously thinking of exporting as Word and then either doing the facing pages stuff there or importing that into InDesign. Both of which are a bunch more work beyond the hundreds of hours I've spent creating this document full of illustrations, tables, and complex layouts. 😢