Hey kiteclone,
I don't know where you are in the country, bu it helps if we know where you are so we can recommend board sizes and types that would be appropriate for the waters and winds prevailing in your local area.
In Perth, we sell beginners in the 70-~87 kilo range a 138 x 42. We consider this a little on the big size, but not by much. For riders weighing more than ~88 kilos up to 110, a sell a 144 x 44, again it is a little on the larger side but allows for good progression and is an easy resell as it is a popular size for beginners.
For riders weighing less than 70 kilos, we suggest a 130 x 40. Beginner boards being a little larger allow for different riding ability and background, it also allows a bigger useable wind range as it gets going in light and can be used in moderate + winds
Most fair dinkum kite shops will have demo boards for you to try before you buy. As a beginner you won't know what is good or bad, so ask a reputable school or instructor, they should be able to help. Forums are a good place to get information, but don't take everything you read as gospel, do your own investigating.
Good winds,