Well, perhaps the story could start with Stiles facing some great danger that forces him to undergo a transformation into an alpha. He might have to battle some powerful enemies and in the process, learn to control his new alpha powers. It could also involve his relationships with other characters changing as he takes on this new role.
There could be a group of hunters who see Stiles as a new threat now that he is an alpha. They might think he will be more dangerous and unpredictable, so they target him. Also, some supernatural creatures that have a vendetta against alphas in general could oppose Stiles.
Partly. The movie takes inspiration from actual incidents, but it's not a 100% accurate account. Some elements might have been fictionalized to make it more engaging for the audience.
Alpha Dog has roots in reality. However, like many movies based on true stories, it might have taken some liberties in the storytelling to make it more engaging for the audience.
Alpha is purely fictional. The plot and characters were invented by the author or creators. There's no real-life basis for it. It's all about imagination and creativity.