Hi Adam,
Here is a one-minute screen capture as well as the scene file.
https://www.amazon.com/clouddrive/share/Y74y26a84eOV2jwg4oxJ8eujRpb2nB9whmVQlrdY4KS
The idea is to use the Landscape object in spherical mode and have four similar objects under the Cloner. While set to blend, you get a lot of variations out of it. I used the Shape>Ellipsoid here, as a moving mesh would have been a long calculation.
With the MoGraph Select option, select the clones that are not useful, and with the Hide Selected art-direction is an easy task.
To your questions:
The Connect object reproduces all children of it as a single new dataset. When I use the Current State To Object, the Connect becomes a Null, and the children polygon object[s].
Yes, I used eight cubes in the first example. But since you like to have more gravel-like results, I dropped the ideas with cubes.
I hope that works for you, and if there is a question, please never hesitate to ask.
I have not included the HDRi map, as you might have your own or pick one from the Content Browser.
All the best, stay safe, stay healthy.