you say you are ocmfortable with a bee 125 so you may want to look at a carve 122, the recommended sailrange is up to 8m?? but i think, if you get yourself a bit of bigger fin you can pull of an 8.5 aswell on it, and you'll be going faster with a bigger sailing range (you could use the 5.5 on the carve aswell).
You can't waterstart you say so i don't know if it is a wise idea to actually buy a kombat already. You can check for second hand boards of similar volume, it'll cost you less, and since you don't use it a lot (you say yourself 30 % of the time) i don't see it as the best buy yet. Once you get to know the techniques then you can transfer to a new kombat but for now i think you can even learn waterstart, harness surfing etc with the carve, there are great boards and the 122 and 133 have more inward footstrap settings which make learning easier and outward for more racing (i'm thinking of the 8.5 in very excellent conditions