It is 100% a great idea to see how you feel about the concept of self-hosting with an old machine. If it’s really old (and I’m talking like anything from before about 2008-2010), perhaps consider snagging an old “tiny”/1L-class box from eBay for cheap. Dell, HP, and Lenovo units can be found for WAY under $100 all the time, and slightly more modern units can still be had at a reasonable price, depending on the model. They’re great platforms to play around with. Just shove a cheap SSD in there and play with it.

Source: an old m920q with an i5-8500T is running proxmox for my home network