To be honest, I don't know for sure. It depends on the storyline and the creators' decisions. You could look for reviews or discussions online to find out.
One great Samurai Jack fanfiction story is 'The Lost Years of Jack'. It delves into what Jack might have been through during his time away from his home. It's really interesting as it shows his struggles and how he managed to keep his spirit alive in the face of so many challenges.
It depends. Some consider them canon if they fit seamlessly into the established Samurai Jack universe and don't contradict the main storylines. Others might have different opinions.
One great Samurai Jack female Jack fanfiction could be 'The Adventures of Female Jack'. It might show her facing different challenges in the same post - apocalyptic world as the original Jack. Another could be 'Female Jack: A New Path' which could explore her forging her own unique destiny, different from the male Jack's journey.