There are three ways to treat gods in your game, and the number of gods can be determined by which one you choose.
1.) Henotheism: This is standard D&D. You believe in many gods, but only worship one of them. Not much can be said about this one that you don't already know from standard D&D. If you choose to go with this one, all you need to do is figure out how many gods you want. The PHP is a nice starting off point.
2.) Monotheistim: This is your Jedeo Christian standard. There is only one true god. If you choose to go with this one, then there is by definition only one god. To make things interesting, you can have people worship various aspects of Him/Her. (Father/Son/Holy Spirit or Maiden/Matron/Crone)
3.) Polytheism: This is the Standard of ancient cultures. There are many gods, and all of them are the patron of a different thing. All gods are woshipped simultaneously by most people. You would have a farmer who is normally a good person giving an offering to the god of evil, simply so that his crops won't be cursed. This one is a really fun one to play with, and I have a list of gods I drew up for use under this paradigm that I'll spoiler at the bottom of my post. You can essentially have a single god for each domain.
At the end of the day, the only person who knows which of these three will work better for you/your group/your setting is you.
Another thing to think about though, is the more work you put into the gods, the more of a central feature you want them to be in your game. You could spend months building a group of gods, and if none of your players play a Cleric, and there aren't any penalties for NOT worshipping a god, then all that work is a little pointless.
Something I have toyed around with in the past, is imposing some sort of penalty/bonus system for being on bad/good terms with your god/the god in charge of your current task. That way, your god has more importance than just a thing that you wrote on your charater sheet.
Slight disclaimer, I used latin as place holders for a great number of them. Feel free to rename them, reflavor them, not use them entirely, or just tell me i'm retarded. Whatever you feel the situation warrents.
Elementa is the god of the elements. He is the oldest of all of the gods, and created the world as we know it. He is depicted as a three headed dragon, with head made of fire, water, and storm clouds, with his body made of stone. His realm is said to be hectic, with an individual passing between standing in a raging inferno and a thunderstorm in the span of a few steps. He is married to Natura, the Goddess of Nature, and together with her they are simply called The Elder Gods.
Natura is the goddess of Nature, and the wife of Elementa. Together with her husband she is thought of as one of the two Elder Gods. She is the second eldest of all the gods, and is linked to plants and animals. She is depicted as a perpetually pregnant woman of approximately 18 years of age. Said to be born of the dreams and desires of Elementa to have a mate to call his own. It is she who populated the world with every beast that walks the ground, swims the waters, or flies the air. Her realm is said to be and endless forest, that contains every creature imaginable, including several not seen in this realm for generations.
Mors is the eldest child of Elementa and Natura, and the goddess of death. She is depicted as a strikingly beautiful girl of approximately 14 years of age. She does not care about reanimated dead, for they are nothing but shells. The type of undead she finds offensive are those that aren’t, those where a soul is still involved. Her realm is the underworld, and she very rarely feels the need to leave it, instead preferring to send her Shepherds to ferry the dead. Her domain is the underworld and her husband is Sanctum.
Sanctum is the youngest child of Elementa and Natura, and the God of Magic. He is depicted as both a loving benefactor and a deranged killer, representing ability of magic to do good or evil. He is married to Mors, the Goddess of death, and is every bit the doting husband. He shares the underworld with his wife, never wanting to be far from her side.
Libra was the god of balance before his fracture. He was the only child of Mors and Sanctum, spending his time between the mortal world, the heavens, and the underworld. He was thoroughly loved by all the gods, and all mortal kind. The day he met a mortal woman and fell in love was the beginning of the end for him. Upon her death, he became quite insane, eventually fracturing into four separate and distinct deities: Bonum, Mali, Gesetz, and Kaos.
Bonum is the God of Good and one of the Four Shards of Balance. He is most often depicted as a monk, who travels the world doing the right thing. He has no realm or mate to call his own, for he spends his time on the mortal plane, doing good deeds. He ventures into the heavens only on the solstice, when the gods convene for councils. His driving life’s work is to show the light to his sister Mali.
Mali is the Goddess of Evil, and one of the Four Shards of Balance. She is depicted as a woman in her thirties, and like her brother, prefers to spend her time in the mortal realm. Also like her brother, she prefers to spend her time attempting to subvert him. It is believed that she does truly love her brother, and merely wants to lead him onto the path of what she thinks to be true power. She does not want what happened to their predecessor to happen to any of them due to their weakness.
Gesetz is the Goddess of Law, and one of the Four Shards of Balance. She is depicted as a knight, wearing gray armor and carrying a morning star in one hand, and a scale in the other. She believes that she is the only person capable of judging the dead for their crimes, and cannot understand why her mother keeps this duty from her. She spends her time attempting to kill her brother Kaos, for only with his death will the world know peace. Her realm is a giant courthouse, and she is its arbiter.
Kaos is the God of All Things Fun if you ask him or the God of Chaos if you ask anyone else. He is one of the Four Shards of Balance, and is depicted as a child of approximately 12 years of age. He spends his time trying everything in his power to liven up things for his bestest friend in all of existence, Gesetz. His realm has shattered the minds of lesser beings who have only glimpsed into it. It is Chaos personified, and he thinks of his grandfather’s realm as Interesting enough by mortal standards”
Perditio is the God of War, Destruction and Strength, the second oldest child of Elementa and Natura, and their eldest son. He is depicted as a breast plated warrior holding a sword in one hand and fire in the other. He has spent his countless eons attempting to win the affections of his sister Mors from her husband. After all, what goes together better than war and death? His realm is and endless battlefield, where warriors are treated to a feast after they fall, only to rejoin the battle afterwards.
Solis is the God of the Sun, and is the second youngest of The Elders’ Children. He is married to Luna the Goddess of the moon, and hates her with every fiber of his being. Ever since her overreaction over aminor indiscretion with a wood nymph which only lasted for a century, he has refused to be in the sky with her at the same time. He is depicted as… well as a giant orange ball in the sky. His realm is his palace at the center of the sun.
Luna is the Goddess of the moon and is married to Solis. Ever since her husband was caught in a “compromising position” with a wood nymph, they have been at odds, refusing to ever be in the sky at the same time. She is represented by the symbol of the moon, and like her symbol, she goes through cycles of complete lunacy. Her realm is a palace located at the center of the moon itself.
Sanitatum is the Goddess of healing and protection, and the only daughter of Solis and Luna. She is married to her half-brother Felicionem and is depicted as a young woman of approximately 20 years of age holding a Cadusa in one hand and a shield in the other. Her realm is a great hospital at the center of a fort. She is the one who brought medicine and healing magic to mortal kind.
Felicionem is the God of Luck, Travel, and Trickery. He is the husband of Sanitatum, and the son of Solis and a wood nymph whose name it is not wise to speak. He is depicted as a gypsie, wearing a long cloak with the hood drawn. He is almost always bored, having been everywhere at least once. His constant hope is to find new places to explore, and that failing to at least spend his time meeting new people. After all, if you can’t go someplace new, hearing a new spin on somewhere you have already been is the next best thing. He loves his wife Sanitatum, for she is the one responsible for playing pranks on Mors on a daily basis.
Libatis is the Goddess of Knowledge and Destiny. She is married to Dolus, and is a daughter of the Elders. She is depicted a sad woman, withdrawn from all those around her. She refuses to make many friends, not able to deal with the burden of knowing the time, place, and manner of their death. There are few whose destiny she cannot read like an open book, and her husband is one of them. She chooses to spend her time in the library created for her by her husband off to the side of his forge.
Dolus is the God of Craftsmanship and Artifice. He is the husband of Libatis, and a child of The Elders. He is depicted as a large man lacking eyebrows and perpetually stained with soot. He is responsible for making the weapons of the gods, as well as crafting the vast majority of their realms. His realm is his forge located at the center of the world.