I have a similar vintage Air, 4GB. I run Debian+i3, though that’s not everyone’s cup of tea. Machine feels quick, except for bloated websites.
ETA: In case you’re not familiar, i3wm is a lightweight, tiling window manager that is very keyboard-driven. I love it, and you might too! But it takes a little getting used to and definitely isn’t a Windows-esque experience.
First thing I’d do is ditch the GUI file manager: get comfortable with cd, ls, mv, rm, etc.
After that, maybe start with basic text manipulation, like grep, awk, sort, uniq, etc. This ties in nicely with IO redirection, which is essential for a “CLI based workflow.” Get comfortable with pipes and file redirection, it’s extremely powerful!
Writing shell scripts is another super useful exercise: any time you find yourself running the same set of commands multiple times, think about making it a shell script. You may end up with some really useful little custom tools that way.
Back in the day I was running GLTron on an Athlon 1800+ w/Nvidia GeForce FX 5200 (I think?) and I was running dual monitors. GLTron didn’t like using both screens since it presented as a peculiar resolution. So I emailed the GLTron dude and he quickly emailed me a patch that let me run the game across both monitors (bezels not an issue because I was doing multiplayer split screen).
What a great game.