The Zephyr B has got hydraulic brakes. Has it arrived yet?I believe the best brakes for hilly terrain are hydraulic brakes. Bikes with torque sensor don't need brake sensors but the rest does. It's a shame that only a few brands make a version with sensor like Tektro and Zoom. It seems the most economical compromise for home builts to be front hydraulic without sensor and rear mechanical disc with sensor. If it were my bike, I'd put something like this to the front:
http://www.ebay.co.uk/itm/Shimano-M395-Hydraulic-MTB-Disc-Brake-FRONT-BLACK-/291217529004