We sort of did this as a family in 2005, sadly before I was an surf-competent kiter. As part of a sabbatical in Cape Town, bought RTW tickets for four (at $21k, largest purchase of my life after my house, and that was a mortgage). Must be a lot more expensive now. Same rules though, so we had time in Europe, then South Africa, then Australia, finally Hawaii and California on way home to Illinois.
I would say the most important thing would be to get better at kiting, especially to the point of being comfortable in the surf. While foiling would be great, dragging a foil with you would be a pain. If you can't do that before the trip, why not start off in late summer in south Texas and cape hatteras to achieve both those goals. Then perhaps Cabarete and northeast Brazil if you can afford a four-continent trip. Then Cape Town for 3 months. Yes, I am biased, but the kiting is so good in Table Bay from December through February there is a reason all the worlds best kiters go there. You will want a car for exploring beyond kiting and various beaches. Yes the water is cold, so you will need to buy a wetsuit, plenty second hand, but the air is warm so it does not feel bad. But it is not a place for beginners. Then if you can afford it, Mauritius and/or Madagascar, and on to Australia, skip NZ, maybe a pacific island, then Hawaii for the summer months, and home late summer.