How do I make applications open on the primary display and not the active display?
I don't fully understand your question but here's my answer on what i think you want to achieve. Make sure you have your display connected when doing the following.


Open the application you want to assign.
Control+Click(Right click) on the dock icon
You should see that a menu pops up and hover over Options
You'll see something that says Assign To and then some options
Select the display you want
You should be done :)