ARE you asking these questions?
Really, I think the answer to all of them is what the effect you're looking for, and the actual one produced, personally.
Where you're venturing is such a personal aspect of aromatherapy, that all these questions are best answered through experimentation. My only concern is the ketone level in Hyssop; that it really should be reserved for anti-viral needs when nothing else works.
But the rest is really trial and error -- applications to the "third eye" and/or temples is common, though diffusing may produce a similar effect. Same with the amount used -- you really want to start at the low end, and work up until again, the effect you're seeking is achieved.
You may compare it to other oils' actions as well: Palo Santo, for example, has a lot of lore around it, and ours is gathered to have the greatest esoteric properties.
I hope this helps! Let me know if you have further questions...