Prof asked to interview me, now I can't get in touch with him - what's the etiquette?
I had similar issues with contacting my future PhD supervisor when applying and found the most efficient route was contacting the assistant. The professor is clearly busy but definitely doesn't want to be inundated with your emails. The assistant may plan his schedule and can book you in. Contacting the post doc isn't as efficient and can look like you are sidestepping the professor.