Congrats on the working system.
I wouldn’t say Linux was sub par or has come a long way compared to other operating systems. It’s always been a better OS than windows but it has different goals. There’s never been a time where a sane person would use a Windows server for example. But with a smaller user base and less hand holding for users, Linux has historically not gotten a lot of mainstream software. Gaming improved almost entirely because Valve threw resources at it.
Driver support has gotten really good though. I’ve been using Linux full time since about 2004. I used to buy hardware with Linux support in mind and it was kind of a pain in the ass. Now I don’t even think about it. Even my printer works with no fussing. I’m not a PC gamer so I don’t have any direct experience but I think Nvidia drivers are the only real pain point left.
A lot of people start with old Dell Optiplexes for self hosting because businesses dump them on the market cheap when they get old. But an old PC will work just fine as a server. I think the 7040 is a good buy, you could maybe go even older. I have a computer with a Haswell era cpu still being useful.
You can find the nicest CPU they’ll take for a couple bucks on eBay too.