Hi there! No, I never put any of my stories behind the Medium pay wall. Nor do I plan to. I often get more readership from outside Medium than from their limited, closed membership, so I don’t see any advantage in blocking access to the general public.
Replying can be confusing sometimes. The interface is clunky, especially on mobile. You should be able to, though, as long as you’re actually logged into Medium. If you’re not, you can’t applaud or comment.
I plan to release a chapter of this piece about every two or three days, and I’m going to tag people who applaud, because Medium’s distribution algorithms are often unreliable. So, you should get notified of each new chapter.