The bigger the betterI like those big resolution to be able to zoom in and see more details. All the models are normal 3d models. I rendered each one with the camera set as orthographic and the background set as transparent and then combined all the objects in gimp and colored the background. I wanted to achieve a more flattish look by doing that. While working with gimp, the ram usage went up to 4 gbEach of the "layers" was rendered with 1000 samples and took about 8-10 minutes each. I used an hdri as lightning source.