Here is a free one.. It seems pretty basic, but it will get you started.

https://www.udemy.com/introduction-to-the-world-of-cisco-for-complete-beginners/?dtcode=iUUkXWi2xg1R

Yes,
A gateway is just a device for getting from one subnet to another (or to the internet) so any device connected this way that has the ability to route is considered a gateway. This really isn't the standard though, unless you have a web filter.

@Rob-Dunn said:

@thanksaj

Yeah, all my experience has been with Windows DHCP, and you're right, configuring the DNS suffix and other options are easy as pie. On the pfSense/Linux side it's a bit...different...!

I don't have much experience with pfsense. I've played with it a little but never actually set it up and used it. YMMV