IMO,because your a light weight (lucky bugger) If you want a mini mal you could start on anything from a 7 foot fun board to an 8 footer,but your weight and coming from a kiteboarding background why not go striaght for a FISH shape!
I am no fish expert so I can't recommend size length,width,depth I will leave that to someone with more knowledge!

If you start on a mini mal,I think you will be looking at trading it in a couple of months,a fish will give you more value for your bucks

mac