I would dought that the stock cable is long enough.
Isn't a 10" a little to much setback for a 150?
When I got my new boat last year I asked the rigger the question as to what size JP I needed.
He said the general rule is 150 - 175's get 6"
200's get 8"
225's get 10"
250's+ get what ever they want.
he said that to much setback will cause the boat setup to lose it's "sweet spot" making it perform worse than without one and especially worse than w/the proper size plate.
As far as motor height start at 3 1/2" below center pad, and go up from there 1/4" increments until you get the performance you are wanting or all it is going to do.
Motor height also depends on style of prop you are running, props such as Merc's Tempest are designed to run at higher transom heights, others will not preform if to high. KENNY