The course will be taught mainly on larger directional board as it is
easier; We do have bidirectional for the latter part of the course for
those students who are more advance. If you want to buy a twin-tip
board, make sure it is around 150 - 160 cm as you need a larger board in
the beginning (first 6 months to a year).
You will be introduced to trainer kites, 2 line inflatables, 3 lines
(foil) and 4 lines inflatable on land. On the water, we only use 4 line
inflatable as you will be already efficient with kites by then and 4
lines inflatable offer more wind range.
I'm impressed and I posted this just to give some props.
BTW, I'll have my own twin tip before the course. I want nothing to do with a directional board. The board I intend to purchase is 140cm, I know it will be a harder learning curve, I don't mind. I don't have loads of cash and can only afford one board.
Hung Vu has been teaching kiteboarding tips online for longer than most people have been riding. His tiered approach that you discribe seems to be well considered. You should learn a lot from the experience.
On the 140 cm board, if you indeed have chronic lighter winds, you might think that one over carefullyr. It doesn't cost anymore to try the various boards that Hung will make available to you. It does cost to buy the 140 cm prior to developing any experience or feeling for board requirements at your weight in lighter winds. Smaller boards are great if you have sufficient wind, if not they can really slow you down, literally!