The gods and ascended powers of Quartus are not a mystery. Other than the Four, the oldest god is just slightly over 200 years old. The entire pre-Cataclysm pantheon (again, except the Four) sacrificed themselves to prevent the Cataclysm from destroying the planes themselves. All of the current gods ascended from mortality after the Cataclysm. The youngest of the major gods is about 150 years old.
Good and Evil--Choosing Teams
Alignment is a property of actions, not of creatures. This includes beings not native to the Prime Material plane (Devils, Demons, Angels, Shadows, etc.). Some beings have more of a tendency toward certain kinds of actions than others, but this is through their own character and choice, not due to inherent nature.
Of course, this leaves the Gods in a strange place. Without alignment to create “teams,” why do they divide the domains between themselves? Do they even do so? How do they divide into pantheons? Do they?
I think the answer is politics. Like all thinking beings, the Gods have different goals. These goals may or may not even involve mortal beings. Gods with compatible goals thus form factions to oppose Gods with incompatible goals. This is similar to an alignment system, but allows much more flexibility. These alliances are alliances of convenience, so they form and break as needed. They also allow Gods who favor different means to similar goals to ally in some ways and not in others.
Why isn’t there war in Heaven? Self-preservation answers a lot of it. They all remember what happened the last time the Gods went to war. No one wants to repeat the Cataclysm War—and no one expects that there would be a winner. This does not mean everyone is all buddy-buddy—there is still conflict, just not out in the open.
Another deterrent for war is the presence of the Four. As the only celestial beings to pre-date the Cataclysm War, they are by far the most powerful of the Gods. They are also a united force that does not participate in any of the factions of Heaven or Hell. Lastly (and probably most importantly) they control and maintain the Great Mechanism, the power distribution system for the cosmos. Access to the stream of power from the Mechanism is what separates Gods from super-powerful immortal beings.
Why the division of labor? Again, the Four are responsible. In return for access to the power streaming from the Mechanism, they require that each God take a segment of the celestial workload, managing some facet of the universe.
Heaven and Hell--Angels and Infernals
The Astral plane is the dwelling place of the gods, the angels, and the infernals. More precisely, the main region of the Astral plane is shaped into a reflection of the Prime plane and houses those beings native to the plane--the angels and infernals. Both races are shaped out of the soul-stuff (anima) which pervades the plane. Before the Cataclysm, angels were followers of cosmic Good and worked to hold back the forces that live Outside and to regulate the elemental planes. The proud Infernals (called Devils then) guarded the Abyssal plane, fighting against the Demons of the Abyss. Since the Cataclysm, "angel" and "infernal" represent political divisions instead of differences in essence. Angels are those that work for the Heavenly Congregation and Choir, gaining a tithe of the Aetheric power for their service. Infernals are "free agents," gaining power from the souls of mortals as well as being paid for running errands on the mortal plane. Pacts and agreements are their specialties. Of the two, infernals interfere more frequently with the residents of Prime, but angelic intervention is more dramatic. Direct conflict between The Celestial Host and the Diabolical Territories and Families is forbidden by the Four; this does not prevent all machinations and intrigue.
The Four are at the top. They are tightly tied into the fabric of the universe. They may be four faces of the same being, or four separate beings that are incredibly close. They do not intervene in the Prime Material and are rarely, if ever, worshiped by mortals. Individually, they are The Maker, The Preserver, The Judge, and The Unmaker. Some claim that they are really one being with four aspects.
The Heavenly Congregation are those gods who have unmediated (except by the Four) access to the Great Mechanism’s power streams. There are 16 of them. These are the gods worshiped across the entire Prime Material. Not all have mortal churches dedicated to them (at least mainstream ones). When mortals speak of Gods, they mean the Congregation. For more information on the worship of these beings, see Religious Rites and Patterns, Part 1 and Religious Rites and Patterns, Part 2.
The Celestial Chorus are the minor gods that are most directly involved in mortal life. They either act as agents of a member of the Congregation or may have a limited domain of their own. They receive power in payment for their services. The number of these is unknown, but probably large. Most of them are best thought of as aspects of greater gods. They may also be ascended mortal heroes. Their worship is regional and situational.
The Outcast Gods are those powerful creatures who have taken up residence in the Abyss (former home of Chaos and its demons). They are also called the Demon Princes. They have seized on power sources outside of the Great Mechanism. They tend to be individually weaker than the other Gods, but still very much more powerful than mortals. They are also unconstrained by the need to play nice. Direct defiance of the Four would get them crushed, but they still tend to interfere with mortals more directly than the rest of the Gods. They do not have domains—instead they have areas of specialization. Worship of the Outcast in Council Lands is strictly forbidden on pain of death. Their worshipers tend to form underground cults. There are five major outcast gods (along with a host of minor god-lings).
The Great Spirits are not considered Gods (as they are tied to the Prime Material) but have power comparable to a member of the Congregation. They are much more localized, however. Shamans and druids tend to venerate (or appease) these beings; savage tribes often make deals with the spirits of the places they inhabit. There are many of these—almost any major land feature has one. Minor spirits are omnipresent throughout all of nature--trees, forests, lakes, rivers, hills, storms, beasts--all of these have spirits. These are the beings with which druids make their contracts for services.