What you need to do is talk to one of the smaller manufacturers, like Doug at Mountain Models, to see what he did. I think he has his kits cut by one of the many small companies that does custom laser cutting.

Getting a copyright is quite simple. AFAIK, all you have to do is indicate that the design is copyrighted on the plan, and it's copyrighted. There's no filing or approval process involved, no central copyright authority. You would file for a patent, but I'm pretty sure there isn't anything on your plane that would qualify for a patent.