Not that i’m aware of. “efficiency” is a matter for a server owner, and frankly if your website is causing issues for the server it will be due to the number of visitors rather than the number of pages, and that’s a “good problem”. (Though potentially an expensive one, as it will require dedicated hosting to resolve.)
Correction to #3: Theoretically, yes. But the number is astronomical. If you have 18,446,744,073,709,551,616 (2^64, or roughly 18 and a half quintillion) pages in your site, you’ve got problems other than Wordpress. Starting with hard drive space.