Re: preventing kit kat update
as far as I know there is no way to prevent the OTA update to download to your device unless you mever use wi-fi. my device is rooted and have a whole bunch of Samsung/Sprint bloatware stopped and frozen, however despite all of that the OTA update still downloaded to my device. you do have a choice after it downloads whether to install or not however and installing it requires you to physically press the button to accept it to reatart the device and install. if you choose not to install however you'll constantly see in your notification panel the system update message.
if you're rooted however you can get rid of that message...