In a way, the characters often do take over.
It is a good idea to know which publishers publish which stories. For example, there is no sense in sending a picture book text to a publisher who does not publish picture books.
Of course there are big differences in length and character and vocabulary, but each level has its particular pleasures when it comes to the words one can use and the way one uses them.
New Zealand is the only country I know well enough to write about. It can sometimes lead to complications.
Every writer has to find their own way into writing.