My friend is a killer surfboard builder but doesn't know what specs a kiter needs for a board. I'm 6'2" & 210 lbs and new to surf style kiting but a 7 year veteran to kiteboarding. The waves I kite on are 3 to 8 footers usually 15 to 20 knots of wind and my kite is 15 m liquid force hi- fi. What size of surfboard should I ride? How many fins? How wide,how long of a board? I want to use it for regular surfing as well for no wind days.

Thats a tough one, the smallest you can possibly surf would be good for kiting If you can use a 6'2"x18 3/4 " for surfing give it nice volume for your surfing and get a 7 or a fast 9 mtr kite.
My own kiteboards have more rocker than average surfboards,where normally kiteboards have a little less rocker than surfboards ,so my guess is an average surfrocker should do the trick (maybe chose a fast one if you can handle it surfwise) give it an extra layer of glass in the stand area and beware of landing areals .