Wow, I can answer the first three questions with one answer. XD
VANELLOPE! Though I love all the characters, I can relate to Vanellope deeply... I have Asperger's and people always shun me or ignore me for it saying that it's a disease, but just because I'm different... I'm not bad... And when Vanellope achieves her dream it inspires me. She also has what may be my favourite line in the film:
Vanellope: "I'm already a real racer. And I'm gonna win."
Technically, though, I love all of the WIR characters equally. I feel like I can relate to all of them so much. Even King Candy and the fellow racers.