I'm not exactly sure of the exact number, but there are a decent amount. You might want to check with comic book databases or dedicated comic forums for a precise count.
Another element in these fan fictions could be the evolution or devolution of the apes and humans. There might be stories that show how the apes' intelligence continues to develop or, on the other hand, how humans are losing their intelligence over time. It gives a lot of room for creativity and speculation.
Well, in new planet fiction, one key aspect is the exploration element. Characters often embark on adventures to discover new planets. These planets might have their own set of rules regarding physics and biology. The stories can also explore the concept of colonization, how humans or other species adapt to a completely new environment on these planets.
In the 'Hitchhiker's Guide to the Galaxy', there is Magrathea. It was a planet - building planet. These fictional planets often have unique characteristics that make them memorable and integral to the story. For example, the harsh environment of Arrakis shapes the culture and politics in 'Dune', while Tatooine's lawless nature provides a great backdrop for the adventures in 'Star Wars'.
Sure, Planet of the Apes is science fiction. It explores themes of evolution, alternate futures, and the impact of science on society, which are common in the sci-fi genre.