Thanks, Smilingcat, I was hoping you would reply.

To be clear, our wireless network is currently at least superficially secure - wireless network is set up with WPA2 security with 18 character password including multiple cases, numbers and characters. And, as mentioned, firewalls are enabled and sharing is disabled, and each of our computers is set up with an admin password - my "everyday" account is actually separate from my administrator account, and my "keychain" (apple user) has a separate password from my login password. And, as mentioned, sensitive docs are stored on an encrypted volume. But, I'm not a computer or security expert and I could certainly have left some door open, even before you let open the network.

Do you feel more comfortable about sharing a network using a router that makes it possible to establish guest networks?