Pointwise Answer is as follows
1.) Is it correct that the TDS deducted is reflected on my Form 26AS only after Step 4 and not after Step 3?
Ans: Yes, Its correct , it will reflect in your 26AS only after processing of step-4 i.e. filling & processing of Form-27Q.
2) In case the TDS deducted does not appear on my 26AS, can I still file my ITR evidencing my TDS credit using the Challan receipt only?
Ans : In challan TAN no. is mentioned (id of buyer not yours), you can not claim it with challan receipt.
3) Which Challan should the buyer use for depositing the deducted TDS for NRI seller? Is it Challan No. ITNS 281?
Ans: Yes, It is the ITNS 281.
4) Can the buyer perform steps 3 and 4 on the same day? In other words, can the buyer submit TDS return using Form 27Q on the same day after depositing the TDS using Challan or does the income tax portal allow TDS return to be submitted only in the next quarter?
Ans : No, It can not be done on same day. It can be filed once Quarter is over.
5) Is any confirmation or acknowledgement slip generated after Form 27Q is submitted by the buyer? If yes, I can ask the buyer to provide me a copy of such an acknowledgement just as a proof of Form 27Q submission.Ans : Yes, acknowledgement slip generated after Form 27Q is submitted by the buyer. You can take a copy from buyer.
6) I would like to avoid the scenario of chasing the buyer to submit Form 27Q after the sale proceedings and hence the reason for my questions above. Is there anything else I can do to ensure avoiding such a scenario?
Ans : This is the process as per Income Tax Act, there is no other option. Additionally Buyer has to also fill Form-15CA before remitting you the sale consideration.
7) In case the sale gets cancelled after TDS deposition by the buyer due to unforeseen circumstances and we are required to execute a cancellation deed, whose responsibility is it then to reverse the TDS deposited? I understand that it is again the buyer's responsibility to submit a TDS refund request from the TRACES website to get his refund. Is this correct? Which specific Form must be used for this purpose for an NRI seller?
Ans : Depends on whether TDS return is filled or not & some other points too, can discuss in detail on the basis of complete information. Once TDS is credited to your PAN No., you have to file Refund request not the buyer.