2): One could combine the paper model and Popular Mechanix plan I posted previously. The model was divided 3'-4'-5' for an overall length of 12', based on a 4x12 plywood sheet. The taper in the rear section is faster on the sides to compensate for none at the top. If I was doing it today it would be 4'-4'-4' with wheelwells in the middle third and straight cut to simplify construction. The middle third would be a cylinder. And the rear doorway would be a Gothic arch.
As for finishing off what you have started:
