The premium data is just a faster version of data available. In one cycle (a month) if you exceed 25gb of data you will go into standard (slower) data. If you use under or stay within 25gb it will always be the premium (faster) data signal. 

The hotspot is not your usable data. A hotspot is when you use your phone for other devices to connect to your device as a mobile WiFi connection. So you get 15gb of data to use the phone as a hotspot, once it runs out you either buy more or turn the hotspot off and wait until next month for a replenish. Note that streaming videos will use an exceedingly high amount of data. Such as 4K Netflix uses about 4gb of data per hour of viewing. A hotspot connection will also be significantly slower than most ISP WiFi connections. 

5G is included in the plan, if your phone has 5G abilities it will automatically pickup the 5G signals and use the 5G when applicable. You need to be around 5G Verizon towers, if the area you're in only has 4G, then it will use 5G and upgrade to 5G within range of the signal providers. If it says it's included; it's no additional cost.