@mayel Three seems fine, until you need the space for something else.
You should probably put sort by likes second, after chronological, since that's kind of the only one that makes sense. Likes usually actually are a signal that means that the user wants to promote the thing within the context of the discussion, the other interactions are not, and I wouldn't want to implicitly convey that these are standard ways to sort discussions, because then users will start treating replying as a promotion signal, and then replying really will become a promotion signal.
And boosting, you may start seeing people boosting things that aren't meaningful when taken out of context, to give it more prominence in-context.
