As for the picks he uses on his instruments, I found this:
'After experimenting with steel picks (which cut his fingers and, being magnetic, tended to shoot pulses through the pickups), Lesh settled on a pick made of titanium. It's really strong and really light, and it doesn't wear out like the Gibson heavies I used to use, he says. The feel of it is superior for the bass -- you hit the string and it knows it's been hit!'
Searching can be so much fun...