I'm asking what is required as it's not clear the requirements to do this.
an estimated minimum requirement would be:
CPU: any X86_64-compatible machine
Memory: 512MB might be enough but 1GB is a better bet
storage: at bare minimum 2GB
these are my estimate for base ISOs
EDIT: :b
didn't correctly checked the title. I imagined you were asking for installation requirement.
Looks like my mirror is using 28GB for packages and 53GB for all ISOs. The space necessary for packages will increase with the addition of new packages.
And you definitely can set up a mirror on ARM, but I wouldn't serve files from an SD card :P