Okay, I picked up what appears to be a Fender Jazz neck, in perfect condition for about $50. Yay! I've decided since I've made such a saving I might as well put together a full bass.

Now, would there be any major worries with ordering a Jazz body off Warmoth or Guitar Mill, and trying to 'transplant' the electronics (sans pickups) as intact as possible from my top-routed Squier jazz? Would it be easier to just do my homework and learn how to assemble a wiring kit?

Learn how to assemble it, it's really not that hard, then decide where you want to go from there...
id make sure you know exactly how to wire first off. as for warmoth, great idea, just make sure you get the right neck routing.
My Gear:
Gibson Faded Flying V
"Dante's Inferno" Iceman
Fender Hot Rod Deluxe 112

Quote by freedoms_stain
I can't imagine anything worse than shagging to Mark Knopfler.

Maybe shagging Mark Knopfler, but that's about it.
If you're doing an all passive jazz bass, the wiring isn't that difficult. The stuff should fit well, you may have to do a little routing for the pickups, but that is all I can see causing problems.