Simplest method for shaping the shell might be using a spreadsheet 3D graph. Most designs start with a flat bottom and curved top which generates lift. Use a profile of an inverted wing NACA shape. The top view would be a 5:1 foil with a Kamm tail. The nose cross-section should be as rounded as possible to reduce the Cd and area exposed to cross wind forces. Angle of attack of the body should be at negative 3 degrees. The windscreen should reach to the shoulder and a center section blend to the top of the helmet front and rear. Use rigid foam insulation to pad the shoulders and hips. An inertial reel lap belt mounted to the frame is worth the effort. Give some thought to internal air flow to the engine. Ceiling tile material and rubber mounts should help the noise and vibration problem. Good mirrors and marker lights help you to see and be seen. If you want to do some wind tunnel testing try a window fan and a 55 gal drum (or the metric equivalent
Good luck mate!