I am currently testing Qubes OS and so far I am impressed, thanks to everyone who contributed to it!
As a Debian user I chose the Debian template on installation and noticed now that the contrib component is included in /etc/apt/sources.list instead of just the Debian default of main and (if needed) non-free-firmware. Is there a reason for it or can the contrib component safely be removed?
I believe nothing form the contrib repo is installed by default. You should be able to disable it.
There might be some kernel non-free kernel packages installed. You could query them with this command:
dpkg-query -W -f='${Section}\t${Package}\n' | grep ^non-free
You will not be able to use your debian template for sys-net and/or sys-usb on some machines. Specifically iwlwifi, brcm80211, atheros and realtek.
And the intel-microcode is not a free software (read this) but is essential for safety and security of Qubes OS. It is even installed in dom0. Here is one example on why it was needed.
Thank you for your answer and the additional information about non-free kernel packages, that’s useful to know!