If I am filing an I-90 due to a name change, can I still efile, and present my supporting documents during biometrics, or do I have to mail?

Don't delay the process.

According to USCIS, in the process for filing your I-90 online, you are to upload your supporting documents. If you do not upload your supporting documents you will be sent and RFE (Request For Evidence) which may delay you case processing. CITATION): http://www.uscis.gov/sites/default/files/images/USCIS-ELIS/I-90_Customer_Process_Flow.pdf