I don't know what the complete version of " 58 Shades of Grey " is. It could be a name or a novel. If you can provide more information, I will try my best to answer your questions.
Yes, it was quite popular. 'Fifty Shades of Grey' started as fanfiction based on the 'Twilight' series. It attracted a large number of readers because of its steamy and somewhat controversial storylines. The idea of exploring a BDSM - themed relationship in a more mainstream fictional context was something that hadn't been done on such a large scale before in this type of popular literature. This led to a lot of buzz and interest, not only among fans of the original 'Twilight' but also among a wider audience looking for a different kind of romantic and erotic story.
The ending of Fifty Shades of Grey is kind of a closure where Anastasia and Christian reach a point of understanding and acceptance. There's a sense of hope and stability for them. However, some might find it a bit predictable or not fully satisfying, depending on their expectations.
Definitely not. Fifty Shades of Grey stands on its own. It doesn't draw inspiration from Twilight. The styles and content are distinct from each other.