WAIT! How much do you weigh? 12-13 will be way to big if you're 65 kilos. 75 kg? Then a 12 will be ok.
A couple of things. You can get into a decent second hand board for around $400, or new for $795.
Wakeboarding and surfing won't help you at all at first. Kitesurfing is like 80% kite skills, so the best thing you can do for yourself is buy or rent a trainer kite. Once you have the kite skills down enough to actually get on the board, then wakeboarding will help.
Also kite sizes are given in area (Square Metres), not length.

Hope this helps
Luke