7: I prefer one at the middle/center and on the fold areas, (mine all match in size), must have a dozen kites built this way by both Bazzer and Shook, but others have used one inch wide strips all along the leading edge, I've seen as many as eleven.
This technique effective doubles the life of your kite's sail (now the trailing edge will wear-out first, that's thousands of hours away, even giving lessons)
Consider covering the knots on the bottom of the sail and locking down the spar so it can't wiggle or even "jump over" the elastic knot/washer
My (extremely shortened) take on this....
We are now entering a state where Rev are the Prism of quad and the quality performance models will be done by skilled craftsman.
The reasons for all of this, the implications, and what the future holds - THAT is the much MUCH longer discussion