Many people wonder, what are the server requirements to run a server on a home computer?
Well the most important piece in running a server is how much ram
you have! Other computer parts do come in handy, but you can always just buy a computer with the good specs.
First off you need ram to run a server. After setting up your server, you can 'java -Xms1024M -Xmx1024M -jar minecraft_server.jar nogui' so this way you can run more players. If you noticed, 1024 = one gig of ram. Each gig of ram dedicated to the server can hold 10 people for sure. If you make it 1024 to 8192, then you would have eight gigs of ram dedicated to the server. That would be able to hold 80 players.
**Tip** I usually add 5-10 extra players to it because you computer is always better than you think.
Second, you should get a pretty good processor. I would say for running servers under 30 players, a Intel Core 2 Duo should be fine. Anything above that should/could be an i5. If you really want to go crazy, use and i7 processor, even though i5 should generally work fine.
Third, you want good amount of storage. Knowing most minecrafters, they LOVE to explore. When someone explores, that is equal to more memory. If you get 20 players exploring, then thats a lot of memory (that is why you should also have a good processor). Depending on how you want to work your server, will depend on how much memory you need. If you have just one dedicated server on a computer, and you don't use it, 100 gigs should be enough (but I would go for more).