I got another nice mac

First thing we did is get a ethernet hub and split our internet connection up.
but we got 7 people in the family and need it so the accounts are networked so they can access there files from the other computer without the floppies.
So i got a few questions
1. how can i do this though my ethernet hub?
2. Any other ways to connect the computers?
3. Is it vulnerable to the internet?
Thanks for the help