I see your edit, and would like to comment that you also haven’t mentioned which rpi you were going to try this on. I recently wanted to set up a quick little pc using a rpi, just so I could browse the web and maybe watch some videos. Tried a rpi2 I had laying around. No way. Moved to a rpi3, and while it would load most pages, youtube was a bust as it completely maxed out the ram and swap. I then went to a rpi4 with 8gb and it has been doable, kind of. Sometimes it’s pretty choppy with the video, but basic web browsing is ok. I did try my plex the other day through the browser and it was barely acceptable. Lots of stuttering and sometimes just hangs, but that’s not the ideal way to view plex on anything. Haven’t tried my rpi5 yet, but my point to all this is that I think you are on the right track setting it up on a spare pc he has. If you had given him a rpi as a ‘desktop’ replacement it might have just soured him on the whole idea.
Spinal Meningitis by Ween.
On a lighter note, I loves me some Señor Coconut.