For example, when I open the [Dom0] Qube Manager, I see that the sys-whonix has 10.137.0.7 value on its IP column. Is this the same in all the QubesOS installs? If I re-install QubesOS from scratch on my computer, or some other computer, is sys-whonix going to have the same IP value?
After looking at the current default Salt States of sys-net, sys-firewall & sys-whonix, I believe answer to your question is No. We see pref settings for label, memory, autostart and some other. But not for ip, ip6, visible_ip & visible_ip6. You should also take into consideration that it is possible to select same sys-vm for firewall and usb during installation. So it makes sense in some way.
Got it. So, the internal IP gets assigned to sys-qubes according to some other logic; perhaps qube creation order. And that logic, whatever it is, can cause the sys-whonix to have some other internal IP from what I have currently.
Yes. And when you think about it, it makes sense. Maybe for example you want 3 independent sys-whonix qubes. One with direct connection to entry nodes, one with connection via obfs4 bridges and one with connection via snowflake bridges. So you could rename the original to something like sys-whonix-direct and create two other ones.
Or maybe you have multiple USB controllers and you want to associate them to different sys-usb service VMs.
Or maybe you have different network interfaces. Ethernet interface connected to corporate sys-net and another for general browsing via 4G interface. Another for Wifi, etc.
Having it not hard-coded is the practical way to do it.