Do you have any old hardware that doesn’t have a job? That is a great place to start. Take some time try out different solutions (proxmox, unraid, casa OS). Then as you nail down your needs you can better pick hardware.

I would keep with what you have. If you don’t have a compelling reason to get something new it’s not really worth it. That is how I try to look at it. Helps me save money and the planet

A few years old prebuilt for the office can work well, I have an HP 290 and HP S01 that work great as servers.