How to use v.net.distance (GRASS) in QGIS?

You do not need to use the CD for the router to function properly, usually these CDs just contain a simplified utility to configure the router, and/or may install some junk programs that may (annoyingly) override stuff like WZC, which I wouldn't recommend.

I wouldn't say don't use the disk, it may have useful utilities on it, but I have never encountered a router that actually straight out required the use of the disk prior to installation.

Since ufw 0.34 ufw supports forward rules.

example: sudo ufw route allow in on eth0 out on eth1 to 10.0.0.0/8 port 8080 from 192.168.0.0/16 port 80

You also need to make sure you have the sysctl net.ipv4.ip_forward enabled. For most distributions, that's done by editing /etc/sysctl.conf and running sysctl -p or rebooting.

ufw doesn't support NAT through it's easy interface, though.

No, most of the time installation discs just make it easier to get you connected to the Internet when installing a new wireless router, I never use them myself, I configure everything manually.

In general it is not a bad thing to use the disc, I am old school and like to configure it myself.