In a word “Yes”. If you can swing the added expense, get a “Troll Master” when you get your kicker. Once you have used one, you will never want to fish without one again.
Absolutely.
If you are out in flat calm conditions, the bowmount will be fine up to over 2mph for a couple hours (maybe). Once you get a chop and/or current, you are going to wish for a kicker. Also a pain in the backside to make big turns while trolling with a bowmount.
They do work together very effectively, the iPilot keeps your heading and the kicker provides the thrust. I almost always use both concurrently.