There is some documentation for TableLayout: TableLayout | GoJS API But I agree that using GridLayout should be sufficient.
The default Diagram.scale for both the Palette class and the base Diagram class are the same: 1.0. Are you sure you haven’t set the initial scale somehow? Have you set Diagram.initialScale, initialAutoScale, or autoScale?
The watermark will go away if you are serving the page from localhost or from the domain for which the license key was requested.