[Wolf20482]

I have 3 old computers in my home. I host my Minecraft server on one of them, the second is used to host backup files, and the third computer is used for WiFi Router by using Pfsense like you said. All my old computers have decent hardware so I can use them for different purposes like I said above. For a webserver, if hosted locally, I would prefer to use a Raspberry Pi instead.

[Honey]

Good ideas but I wouldn't personally recommend running Minecraft servers on an "old" PC. (Tho that'd depend on its specs ofc).

I say that because Minecraft servers are highly intensive when it comes to Processing power & RAM. (Faster Chunk loading requires a good single core CPU & using a high render distance requires high speed RAM). which is why If ur current computer has better specs you'd get better results hosting the server there.

As for web server, that too depends on the internet connection. While a web server doesn't require much specs, Internet speed & Internet stability is a big factor which u may or may not have. I'd personally recommend old computer for LAN related stuff only. (Like you mentioned File Server)

[Decent12]

Actually i don't know about you guys but I had taken great advantage from my old PC since I was interested in PCs from my childhood and wanted to open everything and take a look how it works but no one were allowing me to do that as I had only one PC that time but after a few years I got a new PC and old one was trash so I just decided to separate every part of my PC and open everything to take a look how PC is built.
After opening it up I learnt many things like how processor looks from inside etc but good thing I was able to built it back but it took me almost a week and it helped a lot and still helping since now i am able to fix my PC minor problems and replace it parts if needed.