You should probably skip the neck, given the time you have to complete this project. The idea sounds interesting, but, how did you plan to put frets into sheetmetal fingerboard? Welding, soldering, brazing, or pressing frets into metal would be pretty time consuming and tedious. You could try something like Gittler. (video) Looks like a lot of work, too.
Focus on the body. 1/2" flatstock sounds way too thick, too heavy. I can't remember the name, but, there's a production metal bodied guitar that has sheet metal sides, nicely rolled edges and perforated metal fronts and backs. Specimen makes aluminum guitars fabricated from sheet metal.