The average Netflix user watches 40-50 hours per month, and its going down: https://techcrunch.com/2017/12/11/netflix-users-collectively.... Netflix says 7GB/hour for 4K (~350 gigabytes), but HEVC will halve that number. That's under 180GB, and that's assuming all streaming is 4K, which is far from the case.
That is per account not per person. For a typical household, all other bandwidth usage pales in comparison to Netflix. Youtube, etc., streaming at HD or lower resolutions isn't going to move the needle much compared to the 4K streaming in the calculation above.