I'd suggest to use conventional aluminum siding instead of filon or a flat aluminum sheet. The drawbacks of plastic is that it cracks, fades, and is difficult to repair. Sheet aluminum is very durable but getting it flat and straight across large expanses is a chore. I know RV siding has a reverse lap but I don't see why conventional residential siding can't be used. Maybe I'm wrong on that.
About weight: Estimating weight loss or gain in a situation like you have is nigh on impossible. The good news is that you only have so much area to deal with so substantial changes won't be that big. FWIW, I gained about 600 lbs. with my rebuild. Most of that was in countertops, insulation, and tile. Weight distribution is also a bear but some thought in the locations will eliminate any big concerns. Kitchen areas add weight, as do cabinetry.
If you have a decent frame (mine is fully boxed with gussets) you shouldn't have any issues at the end of the day.
Good luck with the build and keep us posted!
