Should I buy from a bike shop - or go somewhere less expensive?
can you look after your bike? if you can, then you would be better off looking after the bike yourself and you can save some money. Not huge amount but still significant over a long period of time. Don't worry about the electrics, as long as you keep the bike clean and in a dry place, the electrics will be fine.
Is a front hub motor adequate?
Everything is a trade off. Front hub motors are usually very reliable because they are typically lower power and lighter weight compared to the average rear hub or middle motor. However, less weight is to the front, front hub motors have less traction than rear hub motors. If you ride on gravel, you would be better off with a rear hub motor or a middle motor.
How much do you weigh?
How much should I care about brakes?
Hydraulic brakes are always better in the long run. They don't have steel inner cables so they don't rust. They adjust themselves. They are more progressive, require less effort to brake etc. Pads are larger so they last longer too, typically you don't have to touch them for up to about 3,000 miles.
Torque or Speed sensor - I have no idea what these even mean!
For you, cadence sensor. Torque sensor is perfect for those who need a bit of exercise, cadence sensor for those with health impairment.
With a torque sensor, you put in say 50W in pedaling power, the sensor measures that, and tells the motor to give X times your input, 50W, 100W, 150W depending on the selected assist level.
With a cadence sensor, you only have to rotate the cranks to obtain power. The amount of power depends largely on the selected assist level, from 0 to 5.
If you can't be sure you can pedal all the time, a full throttle is very useful. You can start on hill without effort or stop pedaling.
Yes. for your kind of roads, ordinary forks with 63mm travel are OK.
Suggestions:
The Woosh Camino:
http://wooshbikes.co.uk/?camino