1) There are 4 wires in the USB cable, 2 for power, 2 for data. You can be charging and still not have a data connection. Or have a data connection but not be charging. One pin can become disconnected on the charging port in the phone, or the cable could go bad.
2) You can use
WiFi File Transfer to transfer files. Run it on the phone and it'll tell you what to connect to on the computer (you use a web browser on the computer - the app makes the phone become a web server).
3) Kies is good - for something. But you don't have much control over what gets transferred. It's better doing it your way, just the files you want.