Gary,
Definately call the DNR. They were very helpful when I registered my BB3 a bunch of years ago. Since it is homemade you get the opportunity to make up your own serial number, etc. You will need your receipts for materials used in construction. If you payed taxes on those material in Wisconsin you are good to go I think. If you bought material, epoxy, etc. from out of state and didn't pay Wisconsin tax yet - you will have to in the registration process. The state is pretty good about it as long as they get their money - sound familiar? Talk to the Boat Registration folks - they are very helpful and will walk you through it.