A doddle. I've had a couple of these, mine were the ones with solder lugs, so this one, which has the screw terminals will be even easier.
Do it. Honestly these are the best after-market preamps I've ever put in a jazz.
These two are very different beasts. The RS77 are much higher tension than the Nexus strings; if you're going to move to 77s from the nexus then drop a gauge e.g. .105" to .100", that will mitigate the increased stiffness.
Agreed. BSSM is pretty much the perfect album; incredible performances of great songs that were recorded and produced in a manner that embellished all of the above.