Well, I am not certain of the specific answers of each question. The context does not answer the question clearly. It seems at least to show the following:

Two names are applied to this creature in the garden. Satan (later in scripture) and the serpent (in the current context). That does not necessarily mean there are two different creatures, only one creature with two names. The creature seems to be addressed as one and cursed as one by God.

Unless, Satan is indeed now a serpent that runs along on the ground on his belly, which was part of the curse, there must have been more than one entity present. On the other hand, maybe that is the case and has been Satan's basic form (a serpent) since the fall. Is there any place in scripture that would teach the Devils basic form is something else other than a serpent? He may have the ability to be a "shapeshifter" so to speak, but perhaps must always default to a serpent form because of the curse.

That might be the best I can surmise at this point... Thanks... Michael