Is there a way to reduce the redundancy? I would like to install the temp cache with my installer and remove the already decompressed files from the PAR archive.

Yup, its trivial, don't use PAR, use a portable perl , all windows perls are portable they all come with "relocatable @INC", but on other OS you have to turn that feature on when compiling, see Relocatable @INC, see Portable, Re^3: How to create relocatable perl 5.20.1 ? ( reloc_perl)

See createdistribution/createexecutable or cavapackager or just plain portable strawberryperl

Citrus Perl was abandoned

:) not really no, see Why upgrade perl? and https://sourceforge.net/p/citrusperl/code/HEAD/tree/trunk/

5.16.3 is a most excellent version modern perl

If you want a newer citrus perl, for the newest experimental features, well, all you have to do is contact Mark Dootson and make a deal, or compile it yourself

but like I said, 5.16.3 is modern enough