1. Yes. If it's being done. If you pitch cold, though, and use a yeast that doesn't produce much diacetyl, a diacetyl rest isn't always needed. Some do it just as a matter of practice, but I don't. I taste for diacetyl near the end of primary. Diacetyl tastes "slick" or oily in small quantities, and like butterscotch or butter in larger quantities. If there is ANY hint of diacetyl, you do the diacetyl rest.
2. About 10 degrees above fermentation temperature is good. Usually 24-48 hours. You want to do the diacetyl rest when approx 75% of the primary ferment is finished. So, if you're hoping to get to, say, 1.015, and it's at 1.020, that would be a good time to do it.
3. Yes- after the diacetyl rest you rack the beer. Then, start lowering the temperature 5 degrees per day until you're at lagering temperatures.