Debian linux is what many linux distros are based on, the (u)buntu ones being the most popular. Enterprise use may tend to use the RedHat linux, which isn’t debian-based. I’ve only really used debian & previously Slackware, and I’d recommend debian.
I don’t know whether to recommend a PC or RasPi as I’ve never used a Pi. I suspect there must be some limits to it compared to a bog-standard PC that might be a pain as I think it isn’t x86 based. Building a PC from scratch is fun too & could learn what all the parts are.