I don't believe such a tool exists specifically for Ren'Py so you'd pretty much have to do the math yourself especially if you want to make something like Doom. If you have experience with programs such as blender, unity or other 3D software you can use that as a reference imagining every sprite and background as a flat plane.
For a simpler set up like in this example, I use the sprite height as a reference. I might put sprites at zpos -2000 to give me freedom to move the camera closer (especially for 4K sprites). Backgrounds like forests at -10000, and bedroom backgrounds at -5000. Furniture and the like in between these values depending on how close to the characters I want them to feel.