Hi TBA and welcome to the swarm.

I hope that your building all goes to plan and you have your new Mozzie on the water for the start of next season.

Where do you plan to sail/race and what is your sail number ? Any details would be greatly appreciated for addition to the Mozzie register.
If you don't want to make it public just send me a PM through this forum site.
In terms of centreboard width and length there are many variations but most have a width of around 250 mm and a length just greater than 1 m. My current centreboards are 10 inches wide by 1020 mm long. These were cut down from the original timber boards which were much wider and longer and I have seen no adverse effects.
Regards,
Peter