Some things I have learned...
- I routinely have 30 people in chats, in multiple rooms
- don't use chat on a shared hosting service--too CPU intensive beyond five possibly ten people
- there is a special chat daemon that you can install for extra speed, extra capacity. You might visit Moodle Docs for more on that.
- I have never tried to type more than a few sentences at a time, but it should go much more
- the COVCELL project is making a whiteboard for Moodle. Visit Moodle for Language Teaching for more information