1. Why am I seeing models I don't own (advertisement to buy?) randomly on my desktop. I have the settings to only show topless and above.

2. How do I get the models to stay on 1 specific monitor screen. I have 3 screens and when I add more than one model, they show up everywhere (other monitors, on top of windows, etc.) or all stack on top of one another.

1 You are seeing the free previews.
To stop this from happening, go to settings, put a check mark to advanced settings, and scroll to near the bottom. Under 'clips' there is free preview push. Set this to never if you do not want these previews.