Should your book be a series? That depends.Does your story have a natural break point (or several). Are you going to end on a cliff hanger or are you going to have a nice ending for each book?
Series are popular these days. When people like your characters and your stories, they want more of them. However, if your first book isn’t popular, any sequels are going to fall flat.
If you do decide to write a series, plan it out before you start. Think about whether you want people to be able to start with book 2 or 3 and understand the story. Also consider how quickly you can release each book in the series. Will your readers still be interested if book 2 comes out 4 years after book 1?
There’s pros and cons to each style. Just don’t let anyone push you into writing a sequel to a book that really shouldn’t have one.