Just my opinion but 2x3s are enough for studs and 2x4s will hold 1/2 in plywood for roof with rubber over it. 1x anything is very heavy for interior, most use 5/16s tongue and groove. Put your aluminum up on the exterior, wire it, and spray it as is. Take LOTS of pictures so you know where the wiring is before foaming for hanging stuff on the walls. Be sure to foam the floor too. Stud guards are cheap insurance where wiring goes thru studs or rafters. There are better ways for everything but most of us do it this way.