I was out there too.

I was using an 8m Ozone Catalyst with a far bit of trim pulled in. I'm 65 kg and ride a mutant, Shinn wave 148. It was a fairly gusty day but heaps of fun just the same. My bigger kite is 10m.
Keep the long lines, I don't think I saw anyone on short lines. You can definitely ride a smaller kite on a surfboard in the surf.
I think you would benefit from a 9m kite. For your weight 7m on a TT will not be used much.
If the budget doesn't allow a 9m kite think of a bigger board, 148 - 152 range. You can also use it on light days with your 11m. Second hand a good one will set you back about $500.