There are in theory 27 gods (3x3x3), 3 being a magical number in Egyptian culture. There are, however, some exceptions. Other gods and beings who are not part of the official pantheon but who never the less exist.
Ra has withdrawn from the world and the affairs of the gods, but has decreed that no god can have a direct interaction with the mortal world. The gods must act through avatars, or secondary effects (such as weather).
Set has slain his brother Osiris twice now, but Isis has brought him back.
Set was banished by Osiris. So he (Set) fomented a revolt and several gods went with him into exile, to plot the fall of Osiris. These gods are called the Gods of the Desert. Osiris and the other Gods are the Gods of the Yor (Nile river).
There are other beings around however who exist outside the Pantheon, secretive or dark beings who have always been there, or who have been created by the gods and forgotten as failures. These beings tend to worship chaos, darkness and destruction.
The gods can no longer visit the mortal world, but they can manifest themselves in other ways. One option is to have a follower die and pass into the world of the dead. Here the god infuses their divinity into the spirit of the dead person and then returns them to life. The mortal awakens with some of the powers of a god, vastly stronger than they were before.
There is a draw back to this, if the avatar is slain then the god is weakened, what power it gave the avatar is lost. A god may withdraw their divine presence from the subject at anytime, taking one whole action to do so. The benefit to this is that the Avatar will grow in power, and in doing so increases the power of the God.
A god may only ever have one avatar at a time.
Priests gain spells related to the domains of their chosen god. They may ONLY learn powers found in the domains their god supports.
There are a group of powers that are common to all priests, rites of the gods. These will be listed as Common Rites and Specific Rites. All priests can gain these powers, but some may be related to the skill or rank of the priest, as will be indicated.