Mark the envelope and the cover letter with the type of submission. For example, Original Submission, Application to Register Permanent Residence or Adjust Status (Form I-485). Mark the envelope and the cover letter with the form number.
Yes it's beneficial to upload whatever evidence you gather as you go. We uploaded probably 5-6 additional times as we gathered evidence. The more the better and less likely you will get RFE for more evidence.
Mail your forms to the address listed on that form's webpage. You may send your forms through USPS, FedEx, DHL, or UPS. We encourage you to save a copy of your payment, along with any tracking number provided by the courier, for your records and so you can verify the status of its delivery.
USPS provides reliable and affordable international delivery to about 180 countries through Priority Mail International. Most Priority Mail International shipments include tracking and insurance: up to $100 for nonnegotiable documents and up to $200 for merchandise.
Generally, USCIS Mailrooms are equipped to receive boxes / packages and it would generally be a good idea to use one of the flat rate USPS boxes which has similar size to an a USPS flat rate envelope and to send all the documents and copies of attached documents in one box / package to USCIS.
Submitting all required initial evidence and supporting documentation at the same time you file Form I-485 may eliminate the need for us to issue a Request for Evidence (RFE)to obtain additional evidence and documentation. This may also help avoid adjudication delays if we decide that you do not need to be interviewed.
All forms and supporting documents submitted must be single-sided, 8½ x 11 inch letter-size pages.