If you are going to motor around much, I would also suggest getting cruise control. It will save you some thumb or wrist strain.
I bought the amped rear geared motor kit and am very happy with it. The controller has cruise built in, just push the button at it holds the last throttle position. This kit appears to be very gentle on the batteries too. It only draws around 15amps max.
I converted my Giant Suede confort bike. I sit almost upright, no bending over. Very comfortable for this type of ebike.