In my experience the kite size is the least important factor in light wind riding. The board is far more important.
For the kite, anything will do as long as it is easy to keep in the air. In light winds if you drop your kite you're swimming. You really need to understand how to fly the kite in light winds and self rescue is an essential skill. You really can sail across the wind during self rescue. I am better at keeping the kite in the air so I rarely get to practice self rescue. My mate is much better at self rescue than me.
My board choice has changed over the years. Initially I used a 135x49cm TT with virtually no rocker. In later years I used an Airush Sector 60 freeride raceboard. I used these with 12-13m freeride kites.
Surfboards in general are crap for light wind. They have too much rocker. The rocker pushes too much water and makes the board slow. Newer directionals like the North Nugget and Airush Slayer are much better.
Now I ride a hydrofoil and 10m freeride kite. I intend to upgrade the foil soon to something higher performance and I am looking around for a kite to match. Something not too big but light weight to make it easy to keep it in the air and very easy relaunch.
The thing about light wind riding is not so much riding in light wind, which is magic. The real benefit is that you are prepared to go to the beach when it's 10-15 knots and have a real hope of being out riding on days when other people don't go to the beach. 9 times out of 10 those days push up to close to 20 knots are you end up having a monster session with nobody else around.