If you want RadDockZone to resize when add RadDocks you should set only RadDockZone.MinHeight property instead RadDockZone.Height property. You can find a simple example, which illustrates zone without scrollbars (second zone) here:
Regarding your second question, the RadDock has a Height property and it can be easily controled on the server, e.g. RadDock1.Height = Unit.Pixel(400)
As for your last question the answer is no. The RadDock control is a child of the document, e.g. it cannot be dragged outside of the browser bounds.
Let us know if you have any other questions.
All the best,
the Telerik team