I am the person to help you out! What type of data plan do you have?
if you are not on an unlimited data plan and this is your first smartphone, i recommend you download Onavo app its free and you can monitor and watch your usage and have it send you alerts...
Most people don't use alot of data but once you start using a phone, and a new one like the Samsung you are waiting for you might start to use it more than you thought you would. Also most apps use data in the background. You can turn the background data feature off, but if you like emails pushed to your phone, you will need to leave that feature on. But do know data is used by apps running all the time, so turn off and kill processes that you do not need or use. But again, Download the Onavo app and monitor your data usage, after that, explore the apps that are available, get a news app like Pulse.
I can go on and on, for now I will leave it at that. i am sure others will add their own two cents for you. Welcome to the Smartphone era.