Erebus lore does not have Baator, Abyss, etc.
Fall from Heaven is rather strict about the existence of only 21 precepts and only 21 gods (plus their original creator who greatly transcends all, but has chosen to cut himself off from his creations and has not been relevant in a long time). All planes were created by the 21, and strongly bear their mark.
For a canonical description of Hell,
this is the thread you want.
Hell consists of 6 planes, the Vaults of the gods Esus, Mulcarn, Mammon, Camulos, Aeron, and Agares, bound together by connections that could perhaps be considered a 7th Vault owned by Ceridwen.
Bhall now dwells in the lowest Hell, Nyx, the Vault of Agares, along with the King of Hope. She once had her own vault, but it was among the holiest of heavens and was torn asunder when she fell. With Ceridwen's help she may someday be able to bind the pieces of her old heaven into a new vault that will join with Hell, but this may be a challenge as the power of ex nihilo creation was long ago away taken from the gods by The One True God.
There are certainly a myriad variety of demon types, but I'm not sure I'd call them 'races" per se. Most demons are former mortals, who have passed though various stages of demonhood during their metamorphosis. Almost all souls condemned to hell must start as Manes in Mulcarn's mountain before descending into Mammon's city. In the battlefields of Camulos they take on the new form as Spinagons, becoming extremely weak and barely reduced to only their most basic animal instincts as they loose almost all traces of who they once were. Here they must cause pain in order to evolve into stronger demons, before being broken again and made into Imps in Aeron's hell. Only after graduating from this great academy are they allowed to choose a true master for themselves, and to adapt into the sort of demon that would best serve their new lord.
There are also true demons who were created specifically to serve their lord. The least of these are Bhall's Balors. What true demons can do in Erebus is much more strictly regulated by The Compact than what former mortals can. They have lots of leeway when dealing with those whose souls their master owns, but cannot go near a righteous man.
(The heavens are all distinctly seperate vaults, each ruled by one good god. The neutral gods also have their own distinct and seperate vaults, generally not referred to as either heavens or hells. Arawn's vault is unique in that it is easily accessible from Erebus so that the souls of dead mortals can find their way there, and in that he does not so mcuh rule it as allow the subconscious of every soul residing there to make up its own dreamworld. Arawn's Netherworld can be more glorious than the heavens or more terrible than the hells, although for most it has the boring familiarity of the homes they left in Erebus.)
The gods created many other worlds beyond Erebus and their own vaults (some created by one god, some by pairs of opposites or small groups of gods working together), but little is known about them and generally they don't seem to be important. It could be that these worlds had to be cannibalized to create the vaults in their present form, as ex nihilo creation is no longer an option. Ceridwen seems to rule a myriad of worlds, many of which may be the broken fragments of once great planes and others early failed attempts at making worlds.
(I vaguely recall reading at one point that Tebryn Arbandi was not from Erebus in life, but another plane that was similar but had fundamentally different laws of magic and happened to share the same hells. I think that may have been changed a while back though, and is not now canonical.)
There are also infinite planes of pure elements, created by Agares but made accessible by all the gods through the Gems of Creation. Although they denounce him for making these, not a single Good god has refrained from using this power they granted them. Agares hates them for this hypocrisy above all else. While only a third of the gods are in open rebellion to The One and are considered evil, every single one of them has been corrupted and they all fear they will be punished when their maker returns. As a Dark Fantasy, Fall from Heaven does not truly known anything better than a Black and Grey Morality.
Without the Gems of Creation and access to the Infinite Planes the gods might have drained their inner wells of mana to the point that they were left as essentially mortals. It has not been confirmed, but I tend to think that The One intended them to empty themselves of their immense power so that they could come to know the gift of true free will like Mankind has rather than being forever enslaved to the nature of their precepts.
FfH2 already includes 6 more demon lords besides Hyborem. It is strongly implied that while Hyborem is the strongest and is a true demon created as a clone fo Cernunnos, the other demon lords in the game are highly refined former mortals. They already have different emphases, like Duke Sallos being interested in little more than sexual lusts.
