Try things out. Get an old pc with some old hard drives no one will want and get to it!

Just install whatever on it and start asking yourself what you want to do with it.

I started on Ubuntu Server and ended up on Unraid. Caused alot of problems along the way but in the end I learned alot to where I dont stress too much when stuff goes south.

Also, when you truly do invest into a proper server. Consider the drives you are buying are gonna die one day. It may take years to happen but it will happen!