Bear in mind, a system that is built to be a dedicated server will be meant to crunch data. That means 2 things:

• loud fans

• heavy electricity use

If you just want a lab, I suggest getting a desktop PC and loading a server OS on it. Practical hardware experience isn’t too valuable because platforms change and they usually make them super simple to maintenance with lots of online support. Getting a desktop will also save you some bread on initial investment.

I would learn about mtbf if I were you. Everything has a failure point (generally buried deep in product info), and when you start keeping it on 24/7, the hours will burn. Those fans on your GPU will give it up way before they normally would.

Finding a used server is not a good idea either. You aren’t in a data center and servers are super loud. Also, they chew up electricity like a hungry dog and his dinner.

As others have said, find a used desktop somewhere and a cheap KVM switch so you can use the same peripherals for both. It doesn’t need to be beefy by any measure (maybe drive space), just affordable.

For networks, much of it depends on budget and requirement. Do you want home security cameras on your network? Are you someone who works with large files all the time? Do you have gig plus Internet speeds? Do you own or rent? Lots of factors can affect choices. Start from there and build the infrastructure that works for your need. Don’t go looking to build a monster you’ll never really get moving, that’s a waste. Brand will become a factor once you look at the capabilities you need, you’ll see names come up over and over. At the consumer level, there are a few but price is also a factor. Not much help, I know.