Rather than putting the emails in a separate folder why not use the built-in methods to properly manage follow-ups?
Using a follow-up flag lets you say when it needs to be done by, and the emails appear just like to-do items in your to-do list (as well as appearing as normal emails). You can easily sort to-do list by the due date (which is the default anyway), so by changing the due date for a given follow-up you change the order they appear. Flags show in the email view too, and stick to the email even if you move it to another folder.
Overall, I would suggest that ten minutes poking around and learning how to get the most out of using this feature will give you far better returns than moving things around in folders.
Oh, and for the record, no, you can't manually sort, although if you really wanted to you could probably add a custom field "priority" and use that, but that would be lots of work.