With the spheres being too close together, I especially meant the small ones in the front. Spheres are volume of equal width, so they are as wide as they are tall so (unless of course these aren't really spheres and they intersect or come together) they should be as far apart as they are tall.
I understand what you are saying but it doesn't make sense for a 2D drawing—"as far apart as they are tall" in 3D but depends on perspective for 2D.
It's not that I disagree, just trying to figure out a better way to apply the principle than "eye-balling" it. Right now, I see the two small spheres to the left of the front sphere may seem a little too close, but don't see issues with the rest. Also, I don't know if it is placement (too close) that is causing that or the shading or that I made the small spheres all the same size (front should be bigger—copy pasted as didn't want to deal with the mess of non-integer re-scaling)