As for your question how to make the front curves, I would try to treat the front wall the same way you did the roof in the back, i.e. try to create points of steel attachment using the wood frame and plywood, I know it is chicken and egg thing between what goes/set first (horizontal or vertical strips), but the point is to determine where the members will be and where they will meet and welded to created the form, it will require some try and fit excersize on one side and once one side is looking the way you like it, then it can be mirrored on the other side. I was just thinking aloud here, not sure if it helped you..? 
BTW, your work reminded me something interesting, a so-called Hyperboloid structure. The crossing members/strips may create quite a strong structure, one of the known examples of such structure is https://en.wikipedia.org/wiki/Shukhov_Tower, which has unmatched lowest ratio of steel used to bearing capacity for any tower structure. Similar principals are commmonly used in cosmos space exploration structures such as space rocket stages connections/supports, for example.
I am following this build with interest, thanks for sharing it with the board. How are you going to skin this skeleton? I do not think that using aluminum with steel together is a good idea due to a faster (galvanic) corrosion that it would cause
Good luck in your build!
