The harder part of building a Linux distribution/system would be getting to use the hardware you have and exploiting its full potential, especially those that are not built with Linux in mind.

I switched an old Mac to run Linux sometime ago and have documented issues I faced and the limitations I still live with. Most of it is related to decent trackpad support, GUI options for apps/functions I need, and the customization of keyboard shortcuts system wide (coming from OS X/macOS). A lot of information as well as applications I found were simply outdated and not maintained. I've also spent quite a bit of time just to get the system in a shape that's a bit more amenable to me (as opposed to adjusting myself completely to how a specific distribution of desktop Linux works by default). It's nowhere close to perfect for me, but it's the best choice with constant OS/security updates for old hardware that's unsupported by the manufacturer (Apple, in this case).

My advice to anyone wanting to use Linux would be to look for hardware that has been built with Linux in mind. That will save you time, which you can then use to do more productive work/learning (unless your area of interest is in learning about hardware compatibility, developing drivers yourself, tweaking various config files, etc.).