Ive learned on the 550 Fluente, took me around 20 sessions to be able to foil both ways with some confidence. I believe that a bigger wing like the 590 or the Onda will make things abit easier and learning curve faster, specially went you will start trying to do foiling turns. Im not a fan of the shorter mast, i would get a 91 to start and upgrade later for a 101 or 111 depending on what you want to do. Regarding the board, for sure the T60 will make your life much easier then the T38, i did not try the T38 yet but looking just at dimensions it will have less volume and just that will a problem, having a "almost" flat board is also better to start. For me the T40 was the best beginner board.
Please dont think that because your are a competent kiter it will be easy, it WONT! I was doing all the handlepass stuff before i switched almost 100% to foiling and got quite surprise on how much time you need to put on it just to do basic stuff. One year and half later im still not 100% on all the "basic" 4 manouvers required to not fall on the race course, and i probably have close to 200 sessions now.