I posted pics on shielding the other day, by just using aluminum ducting tape... it's a cheap readily availble material (probally not thick enough, but better then nothing). As far as I know, the only two requirements of a shield, is that it can't be attracted to metal & should be at least the thickness as a sheet of newspaper.
Your cavities are already shielded with the paint... it's good enough. By all means go ahead and sheild it further if you want. If I got the stuff laying around, I'll go ahead and add more paint and lay down some copper tape. If I don't, I ain't gonna jump thru hoops to do it.
You don't have to shield the tremolo cavity, because you have no wires carrying a guitar signal thru it. The ground wire doesn't count. A shield is essentially a conductive box that you create to stop electrical magnetic waves from getting into the wires carrying your guitar signal, which would then be carried back to your amp, amplified as noise. Anything metallic act as an antenna and should be grounded. This don't mean you gotta ground every single part, the strings (conduct) do that for you (bridge, tuner, string tree & etc).
Looking at the pictures, I'd only shield the back of ohe pickguard & pickups (never done it on a Jag, never worked on one yet). But feel free to do more, I do some times. There are other things you can do, like not stand next to a flurscent light fixture... stand a bit further from your amp. Use high quality cables from your guitar to amp.
Just tossing an idea out, they make shielded wire. Different aftermarket pickup makers use it. Basically two wires in one, a stranded center core (guitar signal) with a mesh stranded jacket (ground/shield). If I lived alone in a house with 10 cats and had money to throw around, maybe I'd try wiring up a guitar like this... but I won't lose any sleep about it.
