The Samsung updates are really just for the Samsung features. I have a Samsung account and it won't let me even use the apps without updating them. It's not a bad idea to have a Samsung account because certain things like fonts are available in that store and sometimes there's goodies for your phone you can only find there. Also screen mirroring (showing your phone screen on a Samsung tv) needs these updates. Not sure if there is any security issue with not updating them.
Also, to turn o the data feature, go to settings > data usage > and click the date. In that drop down menu it will say Change cycle. Set it to start on the day when your data resets and it will show you how much you have used during that time.
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