Nice work on the guitars, I can relate to a lot of the setups you have pictured.
I used steel in my build because it's 1/4 scale and I wanted it strong. Steel is cheap and easy to fabricate.
If you are determined to do something different, then go for it. I would suggest getting a load of scrap and making a few pieces that emulate the shapes you want to produce and
put them together. Clean the oxide layer off just before you weld or solder. Even the oil from your fingers will effect the join. There are probably a lot of people on this forum with
more knowledge on this subject than me, I will only convey what I know has worked for me.
Post pictures off your efforts.