If the kitesurf bug gets you, you'll plan for maybe a couple of TT's to begin with (and probably end up with 4 or 5!)
A large board transformed my learning, though I only needed it for a few sessions to get going in both directions, I could then use a mid size board fine. It served me well as a light wind board later on.
I have had a ton of boards since, conditions on the day will most likely determine how you get on, though you might be tempted to blame your gear at the time.
Say you have lightish onshore winds and incoming tides. you may have difficulty getting off the beach and need a board with a lot of water contact to get you out.
Same wind, cross on and low tide will see you blasting on a smaller board no problem.
At least with a few boards you can change (assuming you remembered to put a couple in the car!)