Working on some 8700 images from a major project and I erroneously created a Collection and dumped my images into the Collection. Intended to create a Collection Set, as I've customarily done, so that I can break down these images into relevant collections within the collection set. Is there any way to convert this collection to a collection set?
A collection set can only contain collections, so no, you cannot convert a collection to a collection set. If you intended to spread the images over multiple collections within a collection set, then simply delete this collection and start over again. Deleting a collection does not delete images, so there is no harm.