Hi Adam,
For #2–4, I'm not sure what more I can add, aside from an image of my display layout:

Also no idea for #5; as you say, it could very well be environment specific.
For #6, I was able to reproduce the issue when opening Photoshop. The only thing in common between Photoshop and Razer opening is the splash screen, but I've opened other applications without a splash screen without issue before. With Photoshop, however, the reaction is far worse. The taskbar continues to nudge the application over and over away from itself, resulting in quite the display:

Once Photoshop is closed or unmaximised, the visible glitch ceases, but setting a different application to maximised then recreates the rubberband issue, where that new window keeps getting nudged over and then resets itself, endlessly, until explorer.exe is restarted.
If, after that issue starts, I take all applications out of the maximised setting, the visible nudging stops, but the system continues to suffer a performance hit. I wonder if the behaviour is persisting but invisibly, such as the taskbar trying to 'nudge' the Windows screen snapping regions or something, but that is just speculation on my part.
The only other thing I can think to share is my Start11 configuration: