Weighing in from an iPhone (the less fancy model) - with iphones and at&t the only way to get your phone to use no background data is to call att and have them turn the data off completely. I am on a 3 person, 15 gig family plan, which is usually plenty. One month, for no obvious reason, all our phones started using 50% more. We turned off data access for every app, then turned off the global data access from our phones - and the data was still going down.
So, some operating systems will gobble data in ways you can’t control. I have so far stuck with iphones because they work well and last long; my iphone5 lasted over 3 years, and might still be going if I hadn’t dropped it on a concrete floor. My replacement has a case, so I hope I won’t need a new one for some time. I actually bought a prepaid one, then used the sim from our family plan. It cost about US $200 that - way not bad if it lasts as long as I hope.
As far as usage - you’ll be a amazed at how fast you find uses for it. Navigation (you can download map regions ahead of time and navigate in areas with no reception), library books and audio, music, podcasts, getting pics of your friends kids, web browsing. I download Paul’s podcasts when I have internet, and argue with him all through my commute