I'm currently running homebridge and pihole from an older Lenovo (i5, 256 SSD, 8GB ram) laptop (tweaked power settings to allow idle when closed) hardwired into a switch. I am currently running Ubuntu Server LTS, and have uptime ~2 weeks. I'm a little worried about reliability, I was originally using Ubuntu Desktop LTS, and I had an issue with the OS crashing after a 4 days of basically idle...
So my question is, is this a feasible solution? Should I pursue something like a SBC or migrate the machine to an old desktop instead? I don't mind working on the machine occasionally, performing maintenance etc but I don't want to have to troubleshoot the machine on a weekly basis.
I also would like to get into more self hosting, I find it to be super interesting and fun, does anyone have any projects they wouldn't mind recommending or sharing?
Sure. It's plenty feasible. I've used old laptops, desktops, a server board running naked under my desk with parts strewn about... anything can run your homelab.
The only thing you may have issues with long term in a laptop like that is the battery turning into a spicy balloon. Regardless of whether its healthy, or totally "dead" and wont charge, it can and will still start to offgas and can catch on fire. If it has a removable battery, take it out and run the laptop on a normal UPS that is designed to sit fully charged and plugged in 24/7.
Lenovo laptops often have a setting to limit battery charge to 80% which would solve that issue, but I think usually you have to do it from their windows utility software.