There are no hard limits, the framework tries to respect the minimum size of a Dockable, but that does not always work (e.g. because the user makes the JFrame too small). There is no maximum size.
You can set the minimum size, by making sure the children-Components of the Dockable have proper “getMinimumSize/getPreferredSize” methods.
I fear there is no such feature. While it would be possible to implement such a feature, it would take quite some time to do so (we are speaking of several days of work). I personally do not have that time at the moment.
How about putting the CContentArea on a JPanel with a LayoutManager that allows shrinking (GridBagLayout should allow such things)? You could not move around the Dockable, but there might be some empty space. But I don’t think that solution would look good.