Hi FD,
Sanur is notoriously very light. I'd take a 20 and a 16 if I were you. It is also a bit dodgey when the tide is out, so take booties otherwise you will have nasty looking feet.
There are other areas to kite in Bali like Ku De Ta of an afternoon, and Chang Gu early arvie. For them you will need only a 20m or 16m.
I rode Chang Gu on a 12m with a 20 inch wide 6'6" surfboard. Bali hai is windier but at the very end of Bali and getting there is a real mission. Don't even attempt it on a motor bike, you'll be killed by the trucks.
Good luck and good winds, you'll need it,