Hi Ziv,
1. Usually one runs one test project at a time that consists of several test classes and test cases.
2. Yes, the communication is through adb.
3. I'm not sure about wireless, but you can connect several phones through usb and select which one to test.
4. Robotium will print to the android log which you can access through 'adb logcat'.
5. There is no need to have a rooted device.
6. Yes. Most methods in Robotium work by interacting with the app UI. E.g. clickOnText() etc.
For examples please see:
/Renas