you should normalize or apply gain after compression because it makes the overall signal quieter.
it's hard to say what level of compression you will need without knowing how spiky the audio is. see what sounds good. remember that cool edit 2000 gives you a lot of control over compression paramaters - you don't have to use the presets. play around and see what sounds good - for overall mastering, I would suggest not going overboard, unless you're after a particularly "springy" sound (that tight r&b sound is heavily compressed for example).
use the analisys function (not sure exactly what it's called - i'm not in the studio so i can't check it now) over a section of audio to check the dynamic range - it'll give you the highest and lowest db of the selection. you can get an idea of how heavily to push the compression, but ultimately your ears will be the best judge.