How should I start a green reining prospect?

Starting a green colt is all the same, regardless of the end discipline you want to pursue. Your comments do not appear to be those of someone who has the necessary knowledge and ability to accomplish your lofty goal. If you want to learn some basic information, you could check out Clinton Anderson's Colt Starting video. It has some very good information that should be very useful and improve your basic understanding somewhat, it will not qualify you to start green colts, not to be unkind or anything. You do not mention if he has a basic foundation on him, but I would suspect that he does not from your comments. You can't move to advanced training if you have "holes in your training" of your horse. Seems odd to me that a responsible owner would entrust the training of an excellent prospect to someone with such limited experience?? Makes no sense. There is no accounting I guess.