I'll add more when I have time, but one thing I've noticed is that many people don't like the scent of a considerable number of essential oils. If the people involved are more natural living oriented I wouldn't worry, but if it's a group of more 'normal folk' you might want to go with some fragrance oils instead.
This has a few upsides: 1) it's cheaper 2) the fragrance oils are generally more liked and 3) the fragrance oils have longevity and projection characteristics close to that of normal perfumes. Natural perfumes behave completely differently and will likely upset or disappoint people who are expecting something with longevity/projection similar to anything you'd find at Macy's
If you do go with natural oils, I find that a 20% blend of oils into everclear leaves no noticeable alcohol smell, but this is only after the oils have blended together after a week or more of sitting. The alcohol is noticeable at first, and the perfume smells completely differently when initially blended than it will a few days later (and they often keep changing for periods up to a month!).
I believe fragrance oils will blend together more quickly, as there are less chemicals present in them, hence less chemical reactions. That's another plus to the fragrance oils - the smell they get 15 minutes after blending is likely to be close to the final product.