Hi there 
All note components and their comments are stored in tables in the underlying DB which you have access to with an on-premise deployment, but not on our cloud offering. There is not a set limit to the # of comments.
We have an outstanding feature request to add a way for you to access the comments programmatically, but I don't believe this is on our roadmap quite yet. For cases where you need to query the comments or have more control over them, we typically recommend creating your own custom solution with a form + listView or a custom component.