First, my mind is officially blown by the the amount of work that has gone into this Class Library. To make it available free of charge is the kind of generosity you don't see much these days. If there was a "Donate" Button on the site, I would gladly contribute something.
I've spent a couple of days playing with it and I would like to clear something up before I get too far. To create a main window with visible controls on it, it looks like (from the notes within the classes provided) that I should create a GUI Component in IntroJucer, add my controls to it and then use the setContentOwned method of the MainWindow instance of the DocumentWindow.
I think I set off on the wrong foot, adding buttons and sliders directly to my MainWindow Class because that's what it says to do in the book "Getting Started With JUCE".