In general, the Dorohedoro anime is quite true to the manga. It captures the key elements and the unique style of the source material. Some small adjustments might be made for better visual presentation or to fit the animation format, but they don't deviate much from the manga's core.
The Dorohedoro anime ends approximately at a certain point in the manga, but it's not an exact one-to-one match. Some storylines might be slightly different or left out.
The Sao Progressive Vol 1 Light Novel was more about the initial exploration of the Sword Art Online world. It introduced us to the basic rules and the main characters' starting points. But Vol 2 is different. It may have a more intricate plot with more twists and turns. The character growth is more evident in Vol 2. For example, the characters' skills and strategies might have evolved. Additionally, Vol 2 could introduce new elements in the virtual world that change the dynamics of the story, such as new items or abilities that impact the gameplay and relationships within the story.
I don't have the exact count. Sometimes the number of comics in a volume can vary depending on how they're packaged and distributed. You might have better luck reaching out to comic book publishers or libraries that specialize in comics.
The plot often involves the complex web of characters in Ikebukuro. It might continue the storylines of various characters like Mikado, Masaomi, and Anri. There could be new revelations about the Dollars, Yellow Scarves, and other groups in the city, as well as more exploration of the supernatural elements that are always lurking in the background of the Durarara world.