I have a USB I made to install Win 7 on my rMBP. Will the support software that was downloaded when making a USB drive also work with say a Mac Mini or would I have to download new software for every Mac I install Windows on ?
Im not following you what software are you talking about here - is this software intended to run on the Mac? If so, then it should work on any supported Mac, but again, I cant parse what you are talking about exactly.
IIRC starting with 2013 machines, it is specific to that machine. Prior to this, it would d/l the full support package that you could also find at the Apple support site.