With respect to shielding: asked a question about it on Music Electronics Forum / pickup makers. It seems that it's fine so long as you don't inadvertently add a new winding round your coils. This means if you use copper foil then it should be gapped if it's wound round your pickup. This is what is done in transformers with electrostatic shields so sounds plausable.
Back in the stone age I bought a brass pickguard for my cherryburst strat (hey it was the 70's
Thinking about the tone suck it seems likely it was because the brass formed a ring round the pickup and acted as a shorted winding. I haven't tried this yet but suspect that it might be a good idea to put a gap in any conductive paint or foil under the pickguard. A good place would be bottom E side.
I'm about to try shielding on my strat so will let you know how it works out.