I guess so.
It didn’t when we discussed this last time. But at the current state of the developers repository it is required to upgrade to stretch as per these instructions:
The developers repository currently is in a broken state. Getting the upgrade through requires some apt-get / dpkg gymnastics, control-port-filter-python does not work for some reason and networking is broken in the workstation (we might have to port form ifupdown to systemd-networkd). I can notify you once the developers repository is back to a working state and/or when there will be Whonix 14 developers-only downloadabe images.
I don’t know what you mean by that.
For Qubes-Whonix only the IP would be different. The IP of eth1. The checks won’t be required for anything near release.
In fact I have whonix-gw / whonix-ws templates based on Whonix stable-proposed-updates. Then cloned these templates. Made them whonix-gw-dev / whonix-ws-dev. And the derivative template based VMs sys-whonix-dev / anon-whonix-dev. If something goes wrong, I can still use the stable ones.