Personally my double handed backhand works best when it is left hand dominated. In practice I sometimes play left handed for 10 mins just to help get by left arm into the stroke.
As far as the kick serve is concerned, one of the best tips I ever heard was that you should hit your 2nd serve harder than your 1st. I'm not talking about the pace of the ball, I'm talking about racket head speed. If you brush the ball correctly on your kick then the more power you put in, the more the ball should spin. When I really want to get my second serve in I swing the racket as fast as I can manage without mis hitting.
In order to get the correct brushing of the ball, you should toss the ball so that it will land behind you. Then if you lean back to hit the ball, it makes it much easier to brush up the back of the ball. It is possible to do with a regular ball toss, but you need to use the wrist to brush it which I find gives less kick.
Perfect advice. The only thing I would add is really accent the finish.(follow through) Usually when my kicker goes off and the toss is right, the issue is in the finish. Still need heavy accent on the follow through and weight shift into the court.