Fred, miracles might happen.
I think the hard limit is 2^14 - 1 (16383px).
What are your needed W&H sizes?

In the meantime, in #3 above, you mention ~2M objects. That is quite a few, regardless of the size of the final image.
My machine chokes on 132,000 rectangles and they are alternative black and blue.

The only way I can see you working with so much is to have a very large page and put each smaller image on its own layer.
I tried 65536px square and it is almost visible on my monitor at 5% page scaling.
With 4k, you are probably all right.
i have found that even this chokes Xara.

You probably, therefore, need to work on each of the 53 images in separate design files and export each as an image.
You would then need a grid for stitching them back together.
I would make each tile 512px square and basically, have the full 8192px square image stuff into that. You would then have a dpi of 24,576.
Obviously that is barking but you could design when you zoom in to replace the original image at double the resolution and repeat that at each doubling of the zoom.

A fair project.

Acorn