... might be too late here but 154 x 45 would be good. And when you get more experienced, it will double as your light wind board as you will out grow this one soon enough.
Gone are the days where smaller is better. It used to be, ride the biggest kite and smallest board. At my super heavy weight of 120 kg, I rode a 20m North Rhino and a 128cm x 39cm years ago, now I ride 14 or 17m and 144 x 46cm TT.
A bigger board doesn't necessarily mean its a handful either, and will also allow you to ride our skinny gutless tropical winds with an average size kite. Unless your small dude, 10 - 12m are just a little small, 14m is good, especially with a bigger board like the Chopstick.
Anyway, good luck and watch out for them big swimming gecko's!
cheers,
Robbie

p.s. saw the biggest hammer head shark of my life out the front of Gove years ago, Darwin's got nothing on Gove, real wildman country there!