Does this include comments on your own posts? Probably yes. I think it would be better if our own comments weren't included.
It depends how you look at it, because it is also part of the engagement. One of the cool things on Hive is being able to talk with the author, and get replies. :)
The maximum number of posts should be 2.
Yes and no. It depends on the audience and the content. I used to write a lot more and would have engagement across all of them, from different groups of people. Some content resonated with some, others for others.