Their combat doctrine is a lot like the Raven Guard's. Not very White Scar-esque. I believe that the point of doing White Scars or their successors is to play with bikes and make 'vroooom' sounds while you do it. I recommend to make them Raven Guard successors. Maybe Captain Certamen has trouble teaching his newly created chapter the fine art of stealth and ambush. Maybe he is a bad teacher but a better fighter in the field. That could help explain some heavy casualties early in their inception. Then he offers assistance to some Raven Guard, says "Do as they do" and presto (maybe not exactly like that).
NOOOO! The White Scars do not have Dreadnoughts. Their belief is that the warrior's spirit shouldn't be confined to a sarcophagus, but roam free on the plains of Chogoris. It seems very likely that Cartemen would have passed this belief on to the Phantoms.
Another belief is a rather peculiar one; one based on the Dreadnoughts. the Phantoms always honour a Chapter Ancient for his willingness to continue fighting for the Emperor. However the oddity is that the Phantoms aren't optimistic on becoming what they honour. Most Phantoms feel that being encased in a Dreadnought removes what every Phantom relies on - stealth and speed. Because of this there are very few Chapter Ancients in the Chapter, although this may change. Requested development into the structure of a Dreadnought has begun, with enquiries from Viktor on making the Dreadnoughts more manoeuvrable in battle and over terrain. So far it has been suggested that Chapter Ancients have legs shaped like those on an IG Sentinel, but the development is still in progress.