To reinforce what others have said:
- A BBS02 is a solid kit and should be able to meet your needs. I have one and also live in a hilly area and it lugs me all over town. I'm guessing the bike+me weighs ~210lbs. If you're feeling saucy and your budget supports it the BBSHD is also an option, although it'll stress your drivetrain quite a bit more.
- The GT bike you linked will work great. It ticks the disc brakes and solid build boxes.
- The stock chainring supplied with the Luna kit is garbage. Consider the ~$90 for a Lekkie ring as part of the purchase price. I also recommend the Gear Sensor as almost mandatory unless you can be super disciplined letting off power while shifting.
- Gearing: I got the 42T chainring and run a 12-27T 9 speed cassette. Tops out around 30 mph when I spin out (motor could spin much faster) and will also drag me up the steepest hills in Seattle. No trouble with the chainline oddly enough.
- Battery: I have the 52V 7Ah Mighty Mini from Luna as well, and it'll get me somewhere between 8 and 15 miles depending on how hard I'm throttling it. I am running on skinny tires though which I don't recommend and will be changing as soon as I can find a new frame I like.
- If you plan on doing much city or trail riding the "PAS" system on the BBS02 is borderline dangerous since it operates as an on/off switch controlled by pedal spin. Getting full power unexpectedly in traffic or on a narrow trail is no fun. If you have the inclination it's not difficult to get the cable from Luna and disable the PAS so you run throttle control only. This is NOT strictly legal in most places but if you keep your speed down and don't ride like a jackass no one will know or care.
- I'm about 550 miles in on my build and aside from nearly destroying it on some potholes it's been great. Haven't had to replace a single drivetrain component yet with only minimal maintenance.