Most of the time you can find out what is in a product and why it's bad on www.ewg.org if searching for a specific product doesn't help you can search for specific ingredients, i think...
Depends on what you're doing. I know with bleaching if you do little at a time, a few times over the course of a week or even up to a month you can get it all covered, but the damage it causes isn't really worth it and it's hard to wash it all out, seriously hard.