I was unable to find a setting that allows you to be notified automatically of any responses to your posts, and frankly, I'm glad because personally I would not want to be inundated with messages telling me of responses to my posts. But I understand your point; notifications would be nice. Respondents have the option of emailing you through the board using the little envelope icon the the left, underneath your name, but otherwise, you'll have to check for replies. If I wanted a piece for sale, I'd probably email rather than post, but maybe I just have a greater sense of urgency.
As for the number of For Sale posts, people are still posting to the old boards, but those boards are deprecated and should disappear soon.
This forum has a lot of features; I'm still discovering them myself! I understand that it will take some time for people to acclimate.