I understand how hard it is to find the information you need about dosages, length of treatment, what essential oils should be taken and HOW they should be taken. I am working on a post that hopefully will help answer your questions.
The best book I have found that contains this type of information is the "Essential Oils Desk Reference". I will post some more information about this book and also some web site links a bit later. I am on my way out for the day, so it will be this evening.