The standard roPosterScreen is not significantly different than the ASCII art you posted. The biggest hurdle is probably the Menu Buttons.
I suggest trying a simple
roPosterScreenYou LOGO is "<company logo>" and your "SEARCH BTN" and "three "BTN" can be <Categories>. You will lose the Menu BTN, but perhaps they can be implemented as part of an roSpringboardScreen
Your list overlay is a simple (non-transparent) roListScreen, or you can reimplement using an roSpringboardScreen.
You can stack each of the screens (non-transparently) on top of each other as deep as you need, where the top screen gets the user interaction. It will be relatively straightforward if you don't need to exactly copy your UI. Just substitute with available components as needed.