9 times out of 10, I only use my front brake. Just like driving a car, you slowly apply pressure to come to a stop, you don't slam on the brake...if you need to stop more quickly, use both.

Your rear rack looks fairly standard, I'm sure most baskets or panniers would work on it.

As for gears, go with what feels good on your legs, but remember spinning (pedaling at a higher cadence) is better than mashing (pedaling at a slower cadence, pushing hard on the pedals).