Hello, Erin!
To create a forum where only the teacher can start topics but students can respond, without them being notified of all subsequent replies (unless they want to), there's a very practical way to set this up: Optional subscription.
With this option, your students can choose whether to subscribe to the forum or not. If they subscribe, they will receive a notification each time you, as the teacher, create a new topic. They can also choose to "unsubscribe" if they start to feel overwhelmed by others' replies.
Best regards, Eduardo Kraus
Teacher and programmer 👨🏫💻