No, you cannot access it outside of your house.
You are setting up a small LAN (Local Area Network); and a small LAN is sometimes called a TAN (Tiny Area Network). If you wanted to connect to either device from outside your LAN, you would need to enable some kind of remote access; and that is far beyond my abilities to describe online.
And yes, as long as your wireless router requires a password, somebody would need to know that password to get onto your network and send print jobs or access your files. If you really wanted to get anal about it; set all computers with the same logon usernames and passwords. So make sure you username isn't "Hoot" on one PC and then "Hoot_rulz" on the other. Then on the shared hard drive you can setup some specific permissions on the folders.
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