Some of this is getting a bit complicated, more so than need be. The top view of the bike can be tear drop or wing profile with the overall length being 3-5 times the maximum width. The initial angle at the seat back could be less (2-5 degrees) for the first foot back and then taper more to the point. With a 24 in width, 5:1 gives a 120 in. overall length. If you can keep the shape to combinations of conic surfaces, the skin developments are relatively simple.
My favorite shape is from a sailplane design, the SZD-9 bis Bocian 1E.
www.vintagesailplaner.com/Sheet1bis-9.pdf
I truncate or taper the tail to the No. 6 bulkhead length. I scale the canopy profile to come to the top of the shoulder. The nice thing about this design is the fact all curves are combinations of arcs.