#2
I dropped a pair of Duncan Distortions into a very low-end Schecter guitar (that happens to have an excellent fretboard) and the thing became one of my favorite guitars, so dropping a great pickup into an average bass is not at all a bad idea. You may inadvertently create your new favorite bass.
"Maybe this world is another planet's hell?" - Aldous Huxley
#3
Those Rondos make really good mod instruments. I'm planning to swap out the pups on my 6 string some time this summer.
#4
Go for it. The pickup is one of the biggest influences on tone, along with strings. As long as you like the way it feels/plays you can probably make a pretty good bass out of it.

People talk about tone woods so much, but in reality I think they have less of an impact as many people think.
...it was bright as the sun, but with ten times the heat