There is currently only one site setting to set the threshold for both but they do work independently, so you get the topic message for your first two topics as well as the post message for your first two posts. 
- Replies to Discobot don’t trigger the message
- You can use emojis
- The
education.new-replydoes show up when you’re replying to your own topic
You do get the post message for a PM reply as well as a regular topic reply, so that may be something to be aware of depending on when your users start messaging.