I did some research on the Qubes main repository/iso download mirror (ftp.qubes-os.org). There is a brief short page on Qubes OS site with little information on hosting a Qubes OS mirror. Since I used to host an unofficial Qubes mirror in the past, I decided to post this guideline for people who might be interested on hosting a Qubes OS mirror.
Mirroring of Distro mirrors is usually perfored via rsync(1). Qubes source mirror does not provide rsync protocol to the public (or I am not aware of it). But some of its mirrors provide it which makes it perfect for analysis or Tier-2/Personal mirroring. Recommended syncing frequency is not mentioned. This is usually 3 or 4 times a day for release based Distros and is scheduled via a systemd timer/service pair (by comparison, rolling Distros might do it every few minutes via some special trigger!).
Total hard drive space required to host a Qubes OS mirror at the moment is 822.75GB (822,748,334,768 bytes). This info can be obtained prior to the main sync via:
rsync -rtlHnvh --stats rsync://mirrors.kernel.org/qubes
Debian and Fedora mirrors of each release might contain packages for EOL templates. But axing them is most probably not a good idea.
Required bandwidth for source mirrors (not personal) is not documented. This is usually at least 1Gb/s for most Distros.