for shielding, copper foil works well for flat surfaces, like the back of a plastic control cavity plate, and shielding paint works well for odd surfaces and crevices, like pickup cavities. since you're buying new bodies and working from scratch, i'd go with the paint.
aluminum is still plenty conductive compared to copper, as is most any solid metal or alloy. you could use aluminum foil if you wanted, but the reason that is not usually done is that aluminum takes a ton of heat to solder, virtually impossible using a normal soldering iron.
you don't have to solder the shielding, but in order for it to work you must make sure that it all connects to each other [i.e. the foil on the back of the cavity plate must connect to the foil or paint in the cavity], and it all must be connected to gound. usually, the volume and/or tone pots make contact with the shielding and that takes care of it.
Originally Posted by darren wilson
I found that replacing most of the internal wire (everything beyond the pickup wire) with shielded wiring can greatly enhance the effectiveness of any other shielding. On my Dean, the cavity itself is painted with shielding paint, and has aluminum tape on the cavity cover. But it has two long runs of wire up to the pickup selector switch on the upper bout (like a Les Paul).
most guitars have the runs from volume pot to jack and maybe switch to volume pot made with shielded wire, but in a LP type wiring situation like in the Deans, using shielded wire for those long runs is a must. the stock wire in my Dean was shielded, but i rewired it to LP style switching with two volume knobs and had to run more shielded wire for those connections.