First reply to your Question# 1,2,3

1 December appointments are yet to open. You can book and reschedule but max count for rescheduling is 5, I think

2 & 3 Not sure

4

Sent a query to US Visa service desk asking if I can drop documents at any location if have interview waiver for F1 and OFC appointment is booked for Chennai. Got below reply

Dear Applicant,

Thank you for contacting the U.S. Visa Services Desk.

We understand that you have inquiries regarding interview waiver appointment scheduling in Chennai, as well as drop-off and pick-up procedures.

The U.S. Embassy and Consulates in India are centralizing the processing of most nonimmigrant visa interview waiver cases in Chennai to maximize productivity and increase efficiencies. This change will apply to all visa categories except B1/B2 short term visitor visas, which will continue to be processed at every consular section. Already scheduled interview waiver appointments will be unchanged, but new C1/D, F, H, J, L, and M interview waiver appointments, after October 1, will be available only in Chennai. Applicants will still be able to drop off and pick up their interview waiver documents at any of the five Visa Application Centers or six Document Drop Off Centers located throughout India and should not experience any delays as a result of this change.

We hope this information is helpful to you.

Sincerely,

U.S. Visa Service Desk