I am currently looking into adapting an existing website to use a CSS sprite map, as advised by Google Developers. It's my first time doing this and I just need to know a couple of things.

Should the map include all the images that appear or just those which run throughout the site? i.e.navigation.
Should I use mulitple sprite maps? i.e. one for navigation and one for banners which appear on the front page.
What is the best format to use for the sprite map? Gif, Jpeg or Png?
What is the recommended file size limit for a sprite map?
I have several images which have transparent backgrounds. Should I make these into a separate sprite map?

Any help on this would be greatly appreciated.