Well, you can start by trimming some of that stuff at the bottom. If you don't have a dremel I would suggest you get one. They really are worth their weight in gold. If you plan on doing a lot more than just the helmet you will be glad you have one. Get some bondo or other filler to fill in the little imperfections. I use a mouse sander with some fine grit paper to get things smooth. and if you do have or get a dremel you can use that to cut out the visor area. I always hate doing that part but it is not too bad.
also, I suggest buying a metal stalk and a new topper. You can get those for somewhat decent price.