F1 Visa Questions

[mafnadeda]

This is my background: I am applying for a F1 visa to the USA, with a I-20 from a community college. The I-20 states that the length of the program is 3 years. I am planning to transfer to a 4-year university (received a conditional offer already from the university).

1. I filled in my intended length of stay: 4 years (because I am planning to finish my bachelor's degree in a university). Is it fine even though it is different from the one stated in the I-20? Should I bring my university conditional offer letter to prove my intention?
2. I have been to the USA before as a visitor (but the router login visa is on an expired passport). My current passport is empty as I just renewed it recently. How can I tell the visa officer that I have been to the USA (and many other countries)? I believe that my travel history will help me. Should I stick/attach my old passport(s) together with my new one when I hand over my passport to the visa officer during the interview? Note: I have listed the countries I visited in my DS-160 form.
3. Any tips or advice for the interview? Thank you very much for you help.