Hanging Pawns is a YouTube channel I particularly like because it seems to be aimed at average club players, like me, and run by an average club player who aspires to be stronger.
He has done a video on the Falkbeer Counter Gambit in which he considers three black continuations, 3...exe4 (which he says transposes to the Modern Defence to the King's Gambit Accepted), 3...c6 (the Nimzowitsch Counter Gambit which you are asking about) and 3...e4 (the Staunton variation which he considers visually frightening but harmless if white knows what they are doing).
He spends about a third of the roughly 20 minute video on this line which he considers black's most aggressive and challenging option in the Falkbeer Counter Gambit. It is the best online resource for this variation I have found.