If you don't know either of them yet, I'd suggest vim ;)
> I bought an rpi, but could never figure out something to do with it. Any suggestions?
Pi-hole is a super popular project, maybe give that a try.
> or requiring me to understand pointers
Maybe learn to do some old-school stack smashing? https://insecure.org/stf/smashstack.html
There are a bunch of CTFs out there you can play with that help build skills.
> I feel like I'm pointing a flashlight around a cave with Linux systems. Any advise for some systemic learning?
Sounds like you're on the right path :)
Maybe try doing http://www.linuxfromscratch.org/lfs/read.html if you really want a deep understanding of how Linux works.
Also, just browsing the Linux documentation is useful: https://www.kernel.org/doc/html/latest/