Yes. We bought the kit from Woosh and they had done lots of prep work to make sure the cables were the right length for our tandem, etc. You might be able to save a little buying different parts from different people and putting them together, but there are lots of compatibility details to worry about. I certainly wouldn't try that for a first conversion (probably not even now with extra knowledge gained from this forum. I recommend Woosh; they were very helpful with advice before and after buying.
Ours is a front wheel conversion; the bike already had strong steel non-suspension forks and the motor is not especially powerful so we didn't have to worry about torque levers. It took about 1/2 day to assemble, but that was mainly being paranoid about checking details such as the exact right order for bolts/washers/forks on the front. I think if I did another it would be a couple of hours; for experts a lot less still.