In general, the Injustice comics are considered canon to the game. They often provide additional background and depth to the game's universe, filling in plot holes and enriching the characters' arcs.
It depends. In some main comics, injustice serves as a driving force for the story and character arcs. But not all comics focus on it as a central theme. It might just be a subplot or a background element.
The Injustice comics are canon. They form an integral part of the established storyline and have significant influence on the overall narrative and character developments.
I'm not exactly sure. It might vary depending on different editions and releases. You might want to check with comic bookstores or online comic platforms for the most accurate count.