You asked up front about the weight of building in aluminum, and that hasn't been addressed much.
How thin can you get a tube wall? I suppose you would start with pipe then face the ends; bore the inside to your desired ID, leaving a good smooth surface; then turn the outside down giving a good quality surface there too. And you'd check the wall thickness as you go. How thin would you dare to go? The thinner the lighter, obviously.
Now take π∙Diameter×Thickness×Length times 2.7 g/cm³ (density of aluminum). Compare that to the weights of rolled paper tubes you can buy or scrounge; those would be about π×Diameter×Thickness×Length times 1.2 g/cm³ (google's quick answer to "density of paper"). Does aluminum's greater strength let you get down to 44% of the paper tubes's wall thickness, and can you get there without running into machining limitations? Do I sound skeptical? I am.
LOC precision sells a heavy wall tube that's good for 38 mm motor mounts, and airframe tubes for 38 mm min diameter rockets or rockets with smaller motor diameters (most often 29 mm in this context, but not exclusively). That tube's wall thickness is 47.5 mils, so for equal weight in aluminium you'd be at 21 mils. That level of precision in most sorts of cuts? Easy, for an experienced operator like yourself. (Heck, so easy even I might be able to pull it off.) But cutting that as a wall thickness in particular? Sounds more challenging to me, but you're the expert. Worth doing? I doubt it.
Welcome to the hobby and to the forum. And please don't let insensitive jerks like me discourage you.