Nice work , and good effort in showing the practical methods and clear thinking...
i usually make a paper pattern first out of poster board when thats right i make it out of metal using the poster board cutout as a pattern
heaps of stuff on our car was first built as a mock-up by "Captain Cardboard" ( my nick-name for the Rev)....our water tank , fuel tank , every piece of plating in, in fact just about everything because it's all very well to "measure" but when you want to make something as large as possible for a given space it is often easier to start with scissors and cardboard . I used to do a bit of part-time for a repetition engineering works...making hundreds of brackets or thinga-me-jigs...on small runs you don't get the luxury of working out the bugs but the same principles of design apply , minimal cutting , waste and dressing but still coming up with a piece that does the job and is more silk purse than sows ear..