Be aware of cultural patterns in the manner in which people post. If possible, use audio for the instructor feed. This allows the discussion to take place in text while the instructor can still access the auditory senses of the students. Allow some socializing before and after. Possibly have the synchronous chat room constantly available, but post specific times for course discussion.
Many online students are online because of schedule restraints.
Therefore, do not expect to be able to have all of your synchronous sessions at a specific time. Be prepared to stretch sessions out over time with multiple times for each discussion with students organized into groups based on availability. Post an agenda in advance to keep the chat time organized and to give students a chance to prepare. Preface individual responses with to whom it is addressed. Always have a backup plan.