Just to answer a question or two from my experience so people know they're included features:
You can email people who have purchased your product. They have to provide emails, and then itch has a system that allows you to email them a certain amount. I usually only do it when I have a new product out.
You can have forums for your products, but I agree, I wonder if we could have a forum for each of the major itch categories, which could foster some of the community that came from google +.