DB Heroes doesn't follow the manga exactly. It takes inspiration and builds on it, making changes to suit the specific requirements of the series. However, the core elements are still recognizable.
Vegeta is also very likely to be a hero in the new story. He has grown a lot throughout the Dragon Ball series and in DB Legends, he might play a crucial role in fighting new threats. His Saiyan pride and his determination to surpass Goku could drive the story forward in interesting ways.
The length of DB mangas differs. It depends on factors like the story's complexity and the author's vision. Some might run for just a few volumes, while others could have dozens.
I'm not sure specifically what 'db new story' is about without more context. It could be a new story related to a database (db), perhaps a new narrative within a database - related project, like a new data - entry story or a new development in a database system's history.
In my view, 'fiction db' is probably a term used in a particular field or industry related to fiction. It could be a database used by authors, publishers, or researchers to organize and access data about fictional works. But again, we'd need more details to know for sure.