Hello,
I would like to answer your technical questions:
1. There are 2 types of User Reviews in WP Review Pro. They are Visitor reviews and Comment reviews. Visitor reviews do not required comment is enabled.
2. Yes, you can.
3. Yes, there is an option which you can use to show aggregate rating in the rich snippet (schema)
4. You can show both author review and user reviews on the page
My colleague will answer your sale questions soon.
Thank you.