Re: rope length
What jafo9 said!
Get everything ready in your boat how it will be when you are boarding - where everyone will sit, hook the rope up etc., then come up to the speed you like when boarding, then feed the rope handle out to the clean spot on the wake, tie a loop at that point. Simple.
We use a much shorter rope to get to the clean part of the wake, and the kids can jump wake-to-wake easier. We also have a few loops tied in the rope about 3 feet apart so we can make easy adjustments for different riders