Range depends on a bunch of factors, most important- battery/cell type, terrain, speed, gearing, and how much you add to power through pedal assisting the motor. I travel hilly terrain, use a 48V 15 Ah 20 high output ( i think f cell) battery, and have 7 gears. I was able to get 30+ miles when I first got the battery but that dropped off to around 26 after the first year. I don't concentrate on getting the most miles and go fairly fast. I almost always use pedal assist mode but don't try to stretch out the range by going slower and putting more leg power along with the gears. To get 30+ mile range I suggest a 18 to 20 AH battery, mid\standard output battery. 3 speed gearing may be enough with that battery but 6-8 gears would give you better range of gear ratio to get the most effective use of pedal assist, even though you'll find yourself only uses 3 of the gears most of the time.
From what I've read I think the Sick Bike Parts type of mid drive motor setup may allow you to get more range out of the battery than my Bafang BBS02 direct drive. But I don't like the extra chain and gear design, I'm sure it works great for many people but I've seen pictures of people who have had their leg chewed up pretty good.