That depends on the speed of the change and the mass of the bulb. Or vice versa, of course. It just might be easier to leave the bulb and change the room. It's all relative.
Depends. One, if it's an eco-kosher bulb that isn't going to be lit by electricity generated from nuclear power. Two, as long as a man and a woman rabbi have equal turns putting in the bulb. Three, one to change it, one to do a Buddhist mindfulness practice during the change, and one to document the paradigm shift in a best-selling book called The Jew in the Lightbulb. Four, same as above plus an additional rabbi to study the psycho-halachic implications of such a change and then lead a retreat weekend on the experience.
Three: one to write the light bulb removal program, one to write the light bulb insertion program, and one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.