I mostly learned from some of the terminal customization which came stock with Manjaro when I was first learning Linux. So when I made the jump to Arch, I customized my terminal with fsh with the powerlevel10k theme and text highlighting. I also modified some of the default text colors to a green color to evoke green phosphor CRT terminals.
I would say a used Dell or HP business laptop would be a safe bet. Most business laptops have decent keyboards, replacement batteries will be relatively easy to find, and user-serviceable RAM is the norm. Given the not especially high processing power needs, probably the middle-specced ones with a few gens-old i5 will be dirt cheap and work fine for your needs.