I am not sure about the correct answer for question no.1. However, I presume that if any advance receipt is required before transfer of amount by NEFT, the receiver can be asked to affix the stamp on it.
Section 12 of the Indian Stamps Act,1899 prescribes the procedure of cancellation of adhesive stamps as follows:
"12. Cancellation of adhesive stamps - (1)(a) whoever affixes an adhesive stamp to any instrument chargeable with duty which has been executed by any person, when affixing such stamp, shall cancel the same so that it cannot be used again; and
(b) whoever executes any instrument on any paper bearing an adhesive stamp shall at the time of execution, unless such stamp has been already cancelled in manner aforesaid, cancel the same so that it cannot be used again.
(2) Any instrument bearing an adhesive stamp which has not been cancelled so that it cannot be used again, shall, so far as stamp is concerned, be deemed to be unstamped.
(3) The person required by ss(1) to cancel an adhesive stamp may cancel it by writing on or across the stamp his name or initials or the name or initials of his firm with the true date of his so writing, or in any other effectual manner."
Therefore, anyone of the manner mentioned in the post can be adopted.