One manga that could be similar is 'High School DxD'. It features supernatural elements and a focus on a group of students with special powers and their adventures.
The ending of Rosario Vampire manga is quite complex. The main characters face some major challenges and their fates are tied up in a way that leaves readers with a sense of closure but also some room for interpretation.
The Rosario Vampire manga ends with a climactic showdown and resolutions for the main characters. It leaves some room for interpretation but offers a satisfying conclusion to the series.
The Rosario Vampire manga is pretty clean in that aspect. You won't find any nudity. It's all about the supernatural adventures and relationships of the characters.
I don't have the exact figure for how many Rosario Vampire manga books exist. It could be around 10 or more. The series was popular and had multiple installments over time.
I'm not sure if there is such a specific fanfiction where a character from Rosario Vampire is reading Naruto fanfiction. Fanfiction can be very diverse, but this seems like a rather unique and specific concept. It's possible that it might exist in the vast realm of fan - created stories, but it would be quite difficult to find without a more targeted search.