I'm really enjoying watching this unfold.
I've got three single coil P-Basses that I've built similarly to yourself, but I opted for colour finishes (although I've often thought about doing a Paisley finish). I too did the bare wood build, and sprayed the finishes myself in nitrocellulose lacquer at home.
On my basses, I too went through various pickups, before settling on the Seymour Duncan "Stinger" as used by Sting (in his old battered P-Bass), and the late Dusty Hill. It's a stacked hum-cancelling pickup, so needs a 500k pot on the volume, as a standard 250k is really muddy and dark with this unit.
Also, I was looking at your harware parts - are those rear string ferrules the correct size? If they're not, then I have a spare set of the period-correct large ferrules that I could donate as a freebie (as they, and my spare Stinger pickup, are just in my parts stash doing nothing - seems like a waste).