You scuff up existing paint for two reasons. First, you want to get rid of any oil, grease or dirt trapped in the top layer of paint. This is the stuff that cleaners and degreasers can't get off. The second reason to scuff is to set up a physical bond for the new primer and paint to adhere to. You want to give the old paint some tooth so the new sticks better.
Take your time there is no rush. There is nothing wrong with having your project take a couple of weeks.
Painting ceiling does not require premium paint. You can use flat $15 to $20 ceiling paint. I use Sherwin Williams PRO-MAR 200. Painting ceiling requires a lot of physical work and plenty of drop cloths. If you are not up for the challenge or have very high ceilings contacted a professional will prove to be a smart move.
You're not looking for perfection here, but you do want to eliminate every shiny spot of paint. When properly scuffed the paint should have a smooth, but dull matte finish.
Treat yourself to a good lunch and forget the diet. It is amazing what some pizza or a good burger will do for the afternoon painting push.
Another satisfactory whitewash can be made by diluting a moderately heavy cold lime paste (about 33 lbs. of hydrated lime and 8 gallons of water) with 5 gallons of skim-milk.
So how do you know which colors to choose? Thank goodness for Color Me Beautiful. I am sure you remember Color Me Beautiful, a New York Times best seller which sold over 15 million copies.