HI Inorbit,
I pretty much only use a 9m Airush Reactor and a short directional surfboard in all conditions and just change line lengths to suit the stronger or lighter winds, however my style wont suit everyone so I would suggest you get a nice grunty little 12 as I also use on occassion, to help out with the lighter stuff. On a surfboard I can ride from about 10-12 knots with the 12m up to around 15-18 where I switch to my 9m on long lines and stay on the surfboard or switch to a 145 mutant. At around 22-25 knots I change to 20m lines and stay on the either the surfboard or the mutant until around 25-28, above this I ride a normal twin tip of around 135 or mutant and can hold the 9m until around 35 knots comfortably.
Mind you I only ride surf, rarely flat water.
A few guys have 14's over here for lighter winds but a 16m, unless you are a big guy, won't really be necessary. Go a 12 and a 9 or 8. Or if you want a 3 kite quiver a 14, 12, 8 or 9.
Have fun and enjoy, and please respect the local rules and regs both written and unwritten at all spots .... especially public surf beaches!
Good winds