How to list posts based on date?

I’m wondering if this is possible… and maybe a slight “push” in the right direction.

I want to override and/or replace the default WP setting ‘Blog Shows at Most x Posts’ with a custom setting that shows all posts based on a date range set by the admin.

The trick is, I don’t want to break the $paged variable, permalinks (…/page/2), or next_posts_link() / previous_posts_link().

Any “push” in the right direction would be most appreciated. I’m average at PHP/writing plugins.