There's a fair few gods, but most counts of them hover at around 14. Some of them work together: the gods of "Order" such as Sigmar (of humans, Praise Be His Name), Alarielle (of sylvaneth) and Grungni (smiths and duardin, and the one surviving duardin god) have a tentative alliance, as do the gods of Chaos such as Khorne (anger), Tzeentch (change and ambition), Nurgle (dispair and disease), The Great Horned Rat (betrayal) and Slaanesh (desire...who's apparently they've gone missing.) The gods of Chaos and Order predictably do not get along. There's a few harder to catergorise ones, like the aelven gods Tyrion, Teclis and Malerion who are nominally of 'order.' And Nagash, of death. He's very nominally of 'order'.
There's solid documentary evidence that Alarielle, Sigmar, Grungni, Teclis, Tyrion and Malerion all exist. Multiple people have seen them, and the details are consistent enough for things to be fairly plausible. There's less evidence for the existence of the Chaos gods or Nagash , but the gods who definitely exist seem to think they do, and that's good enough for most people.
How interventionist they are seems to vary a bit god-by-god. The aelven gods apparently rescued all the aelves from being eaten by Slaanesh--that seems fairly interventionist, but after that they went quiet. A fair few dwarven accounts make it sounds like Grungni regularly talks to smiths, but that may be metaphor. Sigmar definitely intervenes. He spent a fair few centuries not, and leaving everywhere but his home in Azyr under the depradations of Chaos, but he's back being active. He has an army who has beaten back Chaos. This army is also apparently immortal, magical, made up of people who gave their lives to Sigmar, and made of lightning. Somehow. (Grungni also apparently has operatives. Some them also let a vampire into the library?)
Different gods live in different realms. Generally in fairly innaccessible locations. Accept Sigmar. He has a palace in the middle of Azyr. Any difficulty getting to him is more bureaucratic than physical.
The creation myths--are weird. Apparently there was a world that was--destroyed?--exploded? And Sigmar and co. used bits of it to rebuild this new world, with the help of Dracothion (a ...star drake. A father of star drakes. Whatever that is. The books aren't quite sure either.) Most of the current gods were either gods prior to the world being destroyed, or were mortals who became gods during the destruction.
Unified priesthood? Hahaha. Ha. The various cultures who worship Sigmar can't even agree on how to pronounce his name, let alone anything beyond the broad details of his worship. And that's not getting into all the other gods, with their rival religions. There's places where these rival religions kind of 'get along', in the sense that no one will stop you worshipping Nagash instead of Sigmar, and will merely judge you. Heavily.