charlie brown-
You can also share a printer that is physically connected to only one computer, or even buy a network printer that connects wired or wirelessly to the router, thereby forgoing the necessity of turning on the computer the printer is connected to before printing from another computer.
If you want to get ambitious you can buy network storage as well, which is basically a hard-drive in a case, which connects to the router.
As far as network security, definitely use a WPA protocol.