This is a lot. I will take the questions in order.
A) Why are you changing the handlebars?
On the teal bike I used longer bars that sweep back because those are more comfortable for that rider's proportions and style of riding. She has proportionally longer legs with a shorter torso. The black bike has the original bars. These are both the same model and size. Just different colors. No connectors. No zip ties.
B) On the two wire DC 6V light wires, you could trim them. Keep the rib textured side to the ribbed textured side. That is the positive wire. Seal the splice with heat shrink adhesive tubbing. If you do not want to splice, you can seal the extra wire inside heat shrink tubing. I did this on the bottom of an early build chrome bike and painted it silver. That was before I knew how to really clean things up.
D) You do not need a heat sensor.
E) I use longer mountain pads. Make sure what you use is 100% compatible. Cleaning the rims with alcohol and then acetone will also improve stopping. You will be fine. Stopping is good.
F)
@JRA is correct. It is far better to keep up your cadence. I would disconnect the throttle and the speed sensor to boost performance.
G) Having a spare battery is great. You will always have one that is ready to go.
Side note: That book, The Verifiers is getting better with each page. I am 4/5ths of the way in.