I used to actually know a ton about this stuff but haven’t touched a musical instrument or audio device in over 12 years. Sooooo, bear with me.
All of this will depend entirely where your interests lay in terms of audio production/engineering. One of the core skills would be the ability to pick out different sounds from a soundscape. I suspect you already have a knack for that given how much you seem to think about audio quality. Tied in with that would be an understanding of how digital audio works in terms of bitrate, dynamic range, what clipping sounds (and looks) like, etc. I’m sure there’s tons of info on all that online. Analog audio has a whole other set of skills associated with it, but I doubt it’s super accessible these days for a beginner. That’s outside of cassettes, at least. I’m sure old 4-track cassette recorders are super cheap. As much as I loved analog recording, you’re probably better off just going digitally and using processing to get an approximation of the “traditional” analog sound, though, if that’s your jsn. Or if you’re going for a black metal sound or something else intentionally grungy, go to town on a cassette deck.
From there I’d say the biggest skills would be understanding basic mic technique, the general physics of sound, and how to properly set your levels (basically the ratio of preamp vs amp). Next up would be figuring out basic processing - namely the different types of EQ and compression. Effects play into that too - especially reverb and delay - but EQ and compression (plus proper micing and levels) are generally going to be the foundation of a good mix.
That being said - this all entirely depends on what you’re going for. If you don’t do anything musical yourself and aren’t inclined to record other musicians, you can have tons of fun remixing other people’s work. I’m pretty sure there are sites out there where you can download raw audio tracks to mix yourself. Another viable option if you’re into electronic forms of music is to get a sequencer and experiment that way.
I got my start when I was maybe 13 or 14 with a cracked copy of Fruity Loops (I think it’s called FL Studio now). I used that to write dumb electronic songs despite having no theoretical musical or audio knowledge (besides having previously used the built in Windows sound recording software to layer weird shit I recorded with a crappy mic). That software also came with demo tracks that I experimented with. About a year later I got a bass guitar and started a punk band, and that led to all sorts of weird experimentation with recording mediums. From there I bought a shitty reel to reel tape deck and began recording punk bands out of their jam spaces, eventually went to school for audio engineering, had a bunch of jobs related to the art (while freelancing doing recording work and live sound), and finally burned out and never touched a guitar or mic again.
None of that is necessary or even something I’d recommend. It’s a perfectly legitimate hobby if you want to keep it small-scale. You can start it with almost no money, but that’s where I’d caution you if you have anything approaching an addictive personality - the gear can get super addictive as you begin a quest for the perfect tone. For a few years there I worked at a musical instrument store and most of my paycheck went right back to my work (the staff discount sure helped though). Likewise, most of what I’d make freelancing would go back to gear as well. That’s one of the big reasons I quit cold turkey one day. I still miss it as a hobby, but I know the second I start it back up I’ll be right back to dreaming of expensive tube preamps. Your own mileage may vary if you have better self-control.