In regards to your question about using .035 in place of .028. That's done often. .028 wall anything is of course lighter but also about twice as much a foot as .035. Piper was the king of lightweight. They use a lot of thin bent up channels for many things. Using .035 in place of .028 is not a deal breaker. It saves money.
Thanks for the response, I thought I had read somewhere that some guys used some .035 in place of the .028, I found that it was over twice as much per foot.