I can't stress enough how you want to do this on an old laptop.

I've used RasPis for nodes for several years and 3 different builds now. They always underwhelm when an old laptop would work far better. (And have it's own battery meaning no down-time even in power outages!)

As for the operating system, the best one changes often. Just make sure the one you choose has the apps you want on it and is open source, with a busy community & lots of software contributors. Umbrel seems to be the biggest one of those but the Openness is in question. (Still a great team behind it tho.)