Limited promoted nodes with order
In Views, you can set the number of values returned in the pager config by selecting 'Display a specified number of items'. Have you tried that set to 5? 

If you said something like 'the top 5 in the draggable views list will be displayed' in the help/description that would do it for your users, plus they could then bring back stuff if they wanted without having to go out and reflag it. to automatically unflag content, you could hook into hook_flag() and unflag the oldest or something with some custom php code.

Check out The Flag PHP API, which talks all about that kinda stuff.