When you take your lessons the instructor will choose the best kite size for lesson and afterwards will be able to tell you what combination of kite and board will work for you for MOST conditions...

My suggestion is a 15m (in a C kite) and a "Best Float" board (or something in that size... 132x43cm wide).

I weigh 190 and it works well for most (15-20mph) conditions...

Keep in mind you typically need at least 3 kites and two boards if you want to ride all season. I have 6 kites and 2 boards. I use my 15m 75% of the time, followed by my 21M, and my 13m. Occasionally the 9m, and during a tropical storm, the 7m. If it's blowing 15-18 and I'm in waves, I ride my 18m.