RE: 4 inch or 5 inch vanes
As I understand it, greater vane surface area equals greater control (stabilization) of the arrow so a 5 inch vane would give you more control. However, 4 inch vanes are smaller (less drag) and lighter and do not decrease arrow speed as much as larger vanes.
I am using 4" vanes with a straight offset. My fixed blade broadheads seem to fly just fine and I am getting good clearance through my prong style rest. I think the 5" vanes would be difficult to clear my rest if they were offset at all.
The Mouse