@Ted has valid answers to a couple of your questions. I just wanted to add something referring a bit more to the one he didn't cover as well:
What would it take for an hacker to get into my network?
Really, not a lot. WEP has been pretty much cracked, and WPA/WPA-2 are still not perfect. The way most attackers hack into a WiFi network is with aircrack (which comes with Kali/BackTrack). Basically, they start listening for unencrypted wireless traffic, then pretend to you (a valid user) that they are the router. They "tell you" (as the router) that you need to re-authenticate, so you do. They can't get your password that way, but they CAN sniff the password hash. Now all they need to do is perform a dictionary / rainbow tables attack and they have your password, IF it's weak. But all this allows them to do is access your WiFi. Now, this allows them to do a great many things, but if you watch for HTTPS on logins and use HTTPS Everywhere, have AV, and update your software regularly, it would be rather difficult to compromise your computer or data. However, this changes if you still use the default password for the router management interface. Now they have almost complete control over how your traffic is dealt with, and what it says. Bottom line, as @Ted said, change the password.