This would create a new div layer which covers your entire page.
I would always recommend disabling html, if you are going to enable it best keep an eye on your comments incase someone does post something malicious so you can delete it straight away. Or change the comments so they need approval first.
As for the TinyMCE integrating, I'm afraid I haven't had much time to play around with it, I've had had a quick glance and from what I can see it is possible to integrate with a bit of work but unfortunately I don't have the time to do that. Maybe in a future release of the script I'll look into integrating it.