Hi there loveforoils,
Am loving this thread - you've got some great questions here.
The pure organic essential oils are way more powerful than the perfume quality oils.
2-5 drops in water will last all day (dependent on the size of your room!)
In fact 1 drop in a mug of warm water will last for 2-3 hours minimum.
I would advise against burning any oils- this is similar to putting bread in a toaster - completely changes the properties.
Re: books:
There are 4 schools of thought within aromatherapy-
1.The French prescribe essential oils for therapy, apply therapeutic grade oils neat, and take them internally. Not recommended with the vast majority of oils available in the UK which are pre-diluted and synthetic, high in synthetic phenols, etc.
2.The Germans use oils for the aroma, which sounds like the style you may beinterested in.
3.The Brits (UK) for relaxing aroma massage - primarily by diluting synthetic oils with a carrier oil such as grapeseed, and adulterating them further by burning them.
4.The Americans, who tend to have a similar practice to the Brits, but with a wider range of quality to their oils. Many of their oils are 100% organic therapeutic grade, which they then use for therapy, and apply neat, however, like us they also have no regulation, and also have the cheaper non-organic, synthetic oils, which they use for relaxation with massage.
Most of the books available are geared towards the standard practices with oils dependent on the country of publication. UK books will therefore give a large amount of contra-indications to application of neat oils, etc - purely because the quality of oils is not widely available here, and therefore the research done in the UK is biased to synthetic oils.
Books by people such as Dr Jean Valnet - "Aromatherapie" will therefore be completely contradictory of books by people like Valerie Worwood or Shirley Price.
As with foods, Oils vary in price dependent on quality, and whether they are organic or not.
However, as you noted, the quality shows, and the better the quality, the longer the bottle will last, you need less oils for a more sustained, more powerfull exerience.