You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Maria Hill and Natasha Romanoff related ones using the search bar.
One great fanfiction could be 'Allies in the Shadows'. It shows Maria and Natasha working together on a covert mission. Their different skills complement each other perfectly in this story.
Natasha would likely become more maternal. She'd start to show a softer side that she usually hides. For example, she might be more patient with Peter when he makes mistakes during training, which is different from her normal no - nonsense attitude.
The main differences between Comics Maria Hill and MCU Maria Hill lie in their character development and storylines. In the comics, her role and interactions could be quite distinct from what we see in the movies.
One great 'Natasha Romanoff fanfic' is 'Red Room Echoes'. It delves deep into Natasha's past in the Red Room, exploring her training and the relationships she had there. The character development is really well - done, making it a captivating read.
Well, in the comics, Natasha Romanoff was born approximately in 1928. Different comic issues and story arcs have hinted at this date to provide a sense of her origin and age.