In my extension, an arbitrary number of posts is not offered, only 0 or 1, for performance reasons.
For performance, I didn't want to add a subquery to the visibility SQL query, and the only information available natively is the post number. Is it assumed that the "main" post which is not counted as a reply will be number 1, but afterwards the numbers just count up and might be deleted, so the post number cannot be used to limit to a number of currently visible posts (not deleted or under approval)
For a performant implementation of first-n-posts-visible, an additional column would be needed on the posts table with a pre-calculated value, which is either the post index with any deleted post skipped, or just a boolean visible/invisible calculated by generating the post stream indexes for a guest user model and looking at the first nth post IDs. That logic would then need to run in the background every time a post is created, deleted or restored via an event listener.
