Yeah, you can't use your phone as a key until the car is added to your Tesla account. Once the car is associated to your Tesla account, the previous owner will no longer have access to the car's info and you will then be able to add your phone as a key, through the app.
Projected range is going to vary based on how you drive the car. There is a percentage or mile meter on the main screen that will show you miles based off charge or percentage of battery remaining, based on what view you have selected. If you have it set to miles, this is a basic conversion of Wh (Watt hours) to miles and does not factor in your driving habits, environmental factors, or any other variables that effect range. However, there is another screen you can go to that will project your range based on the last 5 or 15 or 30 miles you have driven. On the bottom of the main screen you will see a ^ in a box, press that and you will get another menu of options, select "Energy." This will give you a graph that shows your battery consumption over the course of the last 5, 15 or 30 miles (you select what mile distance you want). To the far right it will show you a projected range based on you previous energy consumption. This is the most accurate. If you're driving around like a bat out of hell for a day, then your projected range is likely to be pretty low the next time you get into the car. If you drive normal and with the flow for a day, then your projected range will be much higher the next time you get in the car. It all depends on how you drive and the conditions you are driving in. Cold weather and lots of uphill climbs will obviously impact range more than flatter drives in nice sunny weather.
