so most of the gameplay happens on 1 screen but the game is a tycoon like and i need an upgrade screen having said screen would it be against the theme?

As long as you have another "only one" theme. Or you could do the upgrade screen like Downwell's, so that it's just a quick        1    2     3     in the middle of the screen.

what if it would scroll in to the screen or pop up in the main screen as just a part of it