o1bigtenor:
...
> Should I switch my present router from 192.168.1.1 to my chosen
> 172.16.x.x (I'm running on dd-wrt)?

To keep things simple, whatever net you are using locally, make sure
that the isp doesn't use it on the outside, eg. I have seen 10.x.x.x
beeing used on the wan side of routers.

> (Any suggestions for how to learn more about networking without buying
> hugely pricey Cisco courses?)

The classic networking book is
W. Richard Stevens
TCP/IP Illustrated Volume 1
Addison-Wesley
https://en.wikipedia.org/wiki/W._Richard_Stevens
https://en.wikipedia.org/wiki/TCP/IP_Illustrated

A program about subnets and calculation of them
contains text in the code to explain subnetting
http://aspodata.se/computing/ipnumber.tgz

Some headers used in networking
http://aspodata.se/computing/headers.pdf

If you are going deeply into tcp/ip, you'll get to see
https://www.rfc-editor.org/

Regards,
/Karl Hammar