How was Jupiter formed
Maxwell's Smith Prize Essay on the formation of the Rings of Saturn is relevant. Using structural stability as his criterion, he deduced that the 'rings' could only consist of a single almost infinite mass of very small particulates each orbiting in accord with Newtonian dynamics--the correct result as verified by NASA/ Cassini.
 Applying the same approach to a forming  solar system this analysis shows that rings of particulates are a structurally stable attractor for the dynamics, provided the central star is much larger than the mean particulate size.
I am now  well outside my comfort zone so will leave further inferences to others :).
Maxwell's essay on rings of saturn