Hi,
I weigh about 90 kg. My lightwind board ist 150 x 50 cm with 1 cm rocker, my "regular" bord ist 140 x 40 cm with 1 cm rocker which I consider to be a good setup.
I would not go longer than 1,60 m as I encountered difficulties in slowing down the kite with the board when the wind picks up.
I seal my plyboards with epoxy. Less work an good results against humidity, scratches etc. Even better to put 1 layer of 80gr/sqm glass on top an bottom.
The light wind board has ann "hour-glass" shape with a 5 mm sidecut. Beware of shapes beeing too rectangular because the front corner of the edge will dig in water when riding.

Sorry for the late reaction (holidays......). I don't paint the board. I design in Photoshop and print it on thin paper. The paper is laminated on the board with epoxy.

Thanks,
Enzo