CSS seems like a bear but once you get it, you won't turn back. Absolutely use colors like Niki said. I also used borders to keep track of where everything is.
Give yourself some time too. I know you're smart but this is a lot of info.
And don't forget to test in different browsers. I had my pages rolling happily along in IE, did another site, worked great in IE and then someone pointed out a mistake in Firefox, which I didn't have on this puter. It wasn't a huge deal but when I tested my new site, it totally broke in Firefox . It's all fixed now
Tayrak