Hunter has this completely right – it depends on the world. However that may not be that helpful to you, so I’ll tell you what the gods are in my world.
For my homebrew I came to the same conclusion as you – the pantheon/cosmology defines the world. If the gods actually created the world then it needs to reflect their combined personalities. The races in it were created by the gods and their cultures reflect that, obviously with some aligned with certain gods more than others.
I went with a sort of Greek-pantheon feel. 12 gods, 6 male, 6 female. Each rules over a month and the 4 ‘greater’ gods rule over a season as well. They don’t have the Greek pantheon feel in terms of actually coming down to the world and messing around with mortals, but in terms of them being a pantheon with complex interactions between them. Sometimes they will ally with each other based on seasons, sometimes on gender, sometimes on personality. They each have a ‘partner’ in the heavens (spouse, lover, sibling, etc.) so will often work with them, though that may also be a major rift.
I also wanted to discard the concept of ‘worldly’ races being inherently evil, so no more evil orcs, just vicious, barbaric ones. As far as the elves whose coast lines they raid the orcs are evil, but then the Saxons thought the same thing of the Vikings that came over from Scandanavia to rape and pillage.
So to reflect none of the gods have an alignment. This helps toward making them more likely to change allegiances. However to give them more personality each of them has both positive and negative values. Lymos (Lord of Summer) is the god of the sun, war and prejudice, Reaper (Lady of Autumn) is goddess of the harvest, consequences and gluttony. Good worshippers try to avoid/minimise the negative aspects of their deity, while evil worshippers revel in them. And this of course allows me to have holy wars between two groups of Lymos worshippers, or evil priests hiding within otherwise good churches, still able to perform miracles and concealing their more unsavoury activities. Ultimately this gives me more freedom to set up different adventures. Also many priests will be worshippers of the pantheon rather than of a single god, calling on a different god to bring light than to shroud it, but capable of both.
As to cosmology and what the gods are – they are the divine creators of this world. They are physically unreachable by mortals, but can communicate with them when they so choose. High level individuals (not always clerics) may very well be their chosen ones, who reflect their views on the mortal plane.
As to the planes – those are a separate thing. I’ve implemented the planes more as ‘alternate realities’ separated from this world by quantum distances, and by no means bound by anything like the same reality. This means the players can reach them and interact with them.