1) If I recall correctly, any supplement that is supposed to affect the nervous system (i.e. stimulants, nootropics, neurotransmitters, etc.) should always be taken on an empty stomach. But given the fact that you're only having a protein shake beforehand, your stomach should be empty an hour later. So I don't see a problem with what you are currently doing.
2) As far as interactions are concerned, here is a quote straight from the source, Dr. Tim Zeigenfuss (the guy who developed the formula):
"There are no known interactions with herbs or other dietary supps. That said, and as I always say, prudence dictates starting out slowly when combining any supps.
Hope that helps.