Two, one to screw it in, and another to say "Sock it to Me." (Notes: Sock it = Socket. Also, for the infant readers among you, this was a popular catch-phrase from "Laugh In.")
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.
I dunno exactly, but my brother's girlfriend's father's boss's secretary's sister's next-door neighbors' priest's cousin's union shop steward's uncle's Knights Of Columbus club Sergeant-of-Arms's nephew's best friend did it real cheap for me once.