Honestly, it's not a great idea. The regular manga lays the foundation and provides crucial background details that enhance the understanding and enjoyment of Trigun Maxium. Skipping it could leave you confused.
Overall, Trigun Stampede adheres closely to the manga. Some minor details might differ for the sake of the adaptation's flow and visual presentation, but the core remains the same.
The Trigun manga has a considerable length. It consists of multiple volumes and chapters, but the exact number can vary depending on the specific edition and printing.
Yes, it's possible that Maximum Ride could read fanfiction. Just like many fans of a series, the character within the story, if in a more meta - situation, might be interested in reading the creative interpretations that fans have written about their own adventures.