***** NOT A TEACHER *****
Although I never send email, I do receive a lot of it (spam).
It seems to me that people are so busy nowadays that they appreciate short, to-the-point email messages.
In my opinion, your email is fine. But I have made a few suggested changes in order to make it appear more "friendly."
Instead of "What is," I changed it to the contraction. This may make the sentence sound more relaxed and informal and even less demanding.
Instead of "Are there," I changed it to "Do you ...?" This brings Peter into the conversation and shows your respect for his opinion.
I also changed #3 to make it sound more "folksy." "How many people will be attending?" sounds too "cold." "A lot of" sounds more informal than "many."
Student or Learner