The visaScreen requires four types of documents (1)Nursing diploma, (2)NCLEX-RN passing evidence, RN license, or CGFNS certificate (3) English passing scores (you are waived of English scores since you are educated in US), and (4)The application form and fee. Check www.cgfns.org for details. You can apply for VisaScreen earlier by submitting the application form and the fee, then let your school send it your diploma document and RN license or NCLEX-RN passing score later. You may start working on NCLEX-RN exam if you have time. You need to get the approval from the state norsing board for taking the exam. That means you have to apply for RN license of the state you want. NCLEX will verify with the state for your qualification.
I submitted my 485 before I get VisaScreen. My VisaScreen certificate is still in process. I need to pass TSE which is the only one left.
Unfortunately you will subject to the visa quota, and you have to find a way to keep your status legal until you file 485. Check the visa bulletin board each month. The situation may not be that bad as that of India and Philippine. Prepare anything you can at the earliest time you can. Situations are always in change. Good luck.