1) Not sure how CB is related. Can you explain what you meant? The Content plugin won't load the comment box into a user's profile, only into Joomla articles or K2 content. Hopefully it's displaying for you now, since I see it in your 2nd question. If not, again, please let us know a URL so that we can see what's actually being loaded on the page.
2) The height is actually a problem with Facebook's implementation of the Comments box in general. That space is reserved for actual comments, and will grow as more are entered. However, when no comments are entered, there is always room underneath the box for 1 comment to display from the current user, if they add one. It's a bug that's been reported to Facebook many times, but not something we can easily fix in JFBConnect.