I-9 form and reference questions

Hello everyone, I recently got my first real job out of college as an AR/AP specialist for a small startup company. I start December 2. Because this is my first real job I had a couple of questions.

1. According to the formal offer of employment I will be required to complete an I-9 form. I understand this is just a basic background check but should I bring extra forms of Identification such as a passport of birth certificate to go along with my drivers license?
2. Also on the formal offer of employment they said they will need to conduct a reference check. They didn't check references before offering me the job which I thought was strange but this is also my first real job so maybe my understanding of the job hiring process is off. I have 3 references my supervisor from my internship in college and 2 professors? I have been told 3 references is the norm but do you think this will be enough?

Thank you everyone for any information!

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