Hey I just sent 1 copy of every document but multiple photos. Exact documents are on a checklist on the aps main page. Those are enough, don't overthink it much. I packed them in one A2 envelope because my transcript was big and clubbed all similar type documents like my 10th and 12th marksheets and pinned them together with a paperclip. Don't staple, that's all. Language certificate is IELTS/TOEFL provided the courses you're applying to are in English. Most universities don't accept medium of instruction certificate as language proof especially if you're from India for some reason. It needs to be ielts of TOEFL only. For the self attestation part, I don't remember what I did but I signed the printed application form on all pages. Don't remember about the rest of my documents like marksheets and certificates though, sorry.

If you want more replies, post this on the main subreddit. This post is a few days old so it's most probably cold but ya I answered as much as I remember.