Some things which may be left out of the movie:
Problems between Gotti and his wife
Gotti's philandering
Gotti profiting from heroin sales
Legendary gambling addiction
Let best friend Quack Quack die alone because he talked on wire
Am I forgetting anything?
Yeah it definetly will be a fictional account. Junior is involved so I'm sure he will make his father look like Robin Hood. Gotti also had a affair with Sandy Grillo(Neil's daughter) and had a daughter with her.