Heya, sorry missed that question. So what you are trying to do is create a 'Faraday Cage' around your electronics. In the best case scenario everything except the pickup poles is contained within the 'cage'. This isn't always possible, but any shielding is better than none if you are keen to eliminate excess noise and hum.

I'm not sure what you mean by pickup ring? But you can certainly shield the inside of the pickup cavities. I did this on a mates Jazz Bass and it did improve things. You only need to put shielding on the pickguard where it will create a 'lid' for the cavities. So you want a little overlap with the tape out of the cavities so the lid has something to contact to. Also important to earth the shielding.

I've not ordered the PBG shielding tape before so I don't know how much you get. I got a roll from Aust Luthier Supplies that had stacks on it. I've seen people on here use snail tape from the big green shed as well, it's essentially the same stuff, but narrower strips.