The impersonation feature is something that seems important to be very careful with, especially if you are wanting to create a community of people with trust. You could very quickly loose all trust from everyone if you attempt to impersonate someone else.
With discourse there is a staged user feature that works for if e-mails are sent in from an address not registered to an account, that will convert the e-mail into a new topic, which could work great for sending in questions that you could then write answers for.
It would be fairly obvious that you are talking to yourself if you try to have a whole conversation, but starting with writing up answers to generic questions that anyone might ask could work as a way to start.