I'm not that familiar with hub kits since I ruled them out early in my ebike research but for $100 more you could get a 500W cyclone kit from taiwan. I've had mine for 2 weeks and love it. To answer you question about the batteries, yes you would need 4 of those connected in series to get 48v. If you are feeling adventurous you could buy 10 of these thundersky packs and wire them together for a cyclone kit, it would take 20 of those same packs for the hub motor you listed. To take the guesswork out of my battery though, I bought a 24v 20ah battery from pingbattery.com to go with my cyclone, it cost about $430 including shipping. Total cost of my kit was $840 including shipping, that doesn't include any of the add ons and mods I did to my bike. If you want to see my build to know what to expect visit my blog on the build at http://cyclone-ebikedocumentary.blogspot.com/

Pros and cons of a hub motor:
1. you must have a steel fork or the wheel will break loose, aluminum forks are cast and can not handle the torque.
2. you only get one speed with the low end models that don't have gearing.
3. the motor you indicated doesn't appear to have a freewheeling motor so when you run out of battery you will have to fight the motor when you pedal
4. hub motors do have the benefit of easier overall install over other types of motors

Advantages of a non hub cyclone type motor:
1. the motor runs through your rear wheel gears so you get good speed with the ability to climb hills as well
2. you can change gears so your motor is always running at near peak efficiency, makes your battery last longer on the ride
3. because you run through the gears a lower wattage of motor will give the same results as a higher wattage hub motor. (I have seen videos of people using 1000W hub motors to achieve the same results I get)

Disadvantages:
1. more complex install, be prepared to sweat a little
2. the bike has a motor attached that looks like a motor so anyone that sees the bike will know it is electric.