I want add a power system to a Day 6 Journey (7 speed Shimano Nexus internal gear hub) or Journey EX (7-speed Shimano derailleur). In the event that I choose a mid-drive power system (e.g., Cyclone 500-watt kit ($495)), then I would choose the Journey EX over the Journey because I am concerned that the 7 speed Shimano Nexus internal hub drive may lack the durability to withstand the combined pedal and motor power. In the event that I choose a front hub drive (e.g., Front BMC V2-S 600W High-Speed Motor with Torque Arm ($669)), then I would choose the Day 6 Journey with Nexus hub because I prefer it to the derailleur gearing.
I live in Las Vegas, which can be both flat and hilly, but I am not seeking mountain bike gearing.
I would appreciate comments concerning the two configurations that I have described above as well as other suitable configurations. Also, I would appreciate comments concerning LiFePO4 battery selection: 1) 24, 36 or 48v, 2) brand of battery and 3) an online store where it can be purchased. I realize that battery prices vary with quality, discharge rate, etc., and I am looking for a good balance between price and quality.