For your first question about having the avatar walk around, set the marker to be a global marker. Then add the walk action. The marker will be used for the origin and you will not need to link the two.
Code:
marker = camera.addMatrixMarker(0,width=1000)
camera.setGlobalMarker(marker)
Regarding the error, what kind of graphics card do you have? Do you have the most recent drivers?
Try adding a second window like this.
Code:
ar = viz.add('artoolkit.dle')
subWindow = viz.addWindow(pos =[0,0.2])
ar.addWebCamera(window=subWindow)