Hi Guys,
You really don't need to know how to kite to learn foiling. Behind the boat is the trick, it will teach balance and the finesse of trimming the pitch.
Reasonable kite skills are important. You just need to be able to fly the kite without looking at it. Your focus will be on the foil. Having said that, you could learn good foiling skills behind the boat and then have basic kite flying skills and still succeed.
When learning behind the boat you have to contend with the water start which is by far the most difficult part, but once you are up, its really easy to learn pitch control and stability.
By learning on a kite, the water start is really easy, but pitch control and dealing with speed and balance is really difficult. Riding downwind is very challanging.
I would say that learning behind the boat is the safest and quickest way to learn because when you crash, you simply let go of the handle and you stop, a botched water start on the kite means too much speed, a foil usually in the air and you are towed along by the kite for "a ways".
The short cut to success and progress is behind a boat for an hour, then take your new knowledge to the kite and you will be up and away.
DM