Hey @garrett.mccurrach,
You can do this by having the messages repeating group sorted with these settings:
Sort by: Creation Date
Descending: No
This will put the oldest posts at the top, and the newest posts at the bottom.
To accomplish Facebook-style scroll, you can create two custom states which automatically cause the page to scroll to the bottom of the repeating group anytime a new message is created. Airdev created an awesome messenger example, and the custom state scroll example is in this thread as well:
Messenger Example:
Custom States setup: