The Redding body die has no expander it sizes only the body and shoulder.
It can be used before or after the Lee collet die, neither of them has any effect on the other.
The part of the Redding die where the neck goes is larger than a fired case neck. Actually, they also work really well for forming larger necked cases into smaller. For instance, 7mm-08 into .243AI. The neck part of a 243 body die is smaller than a 7mm case but larger than 243. It will size the 7mm neck down so that it fits into a 243 sizer perfectly.