Definitely shield the cavities - that's one of the best, cheapest mods you can make to a bass.
series/parallel is a great option for a more punchy, mid-range sound.
I've put Wilkinson pickups in all my basses (J, P and MM), and much prefer the sound of them to the 'Duncan Designed' that some of them came with, but it's like a singer' microphone choice - there's just no alternative to testing out as many as you can and finding which ones work best for you.