Great to start on a P Bass - started there myself! Jigsaw is fine - take your time to clean it up afterwards.

Nut - makes it easier to replace with bone - otherwise a drop or two of superglue and you're good to go.

Pickups can be better than expected - have kept about half of mine so far, others I've replaced. They're easy to do - so you can hold off until you've wired it all up and see if you like the sound.