f6 this early is unusual but fine, usually you see bf5 and then f6 or bf5, e6 then f6. Black will usually play ne7 and depending on how white plays will decongest his position in different ways (but g6 gg7 is rarely a good idea) if black can take on e5 and then ng6 he is usually well and will castle either side.
f6 in the Nimzowitsch

As I’ve begun adopting the Nimzowitsch Defense as my main defense against e4 by white, I’ve discovered a very interesting line in the Scandinavian variation in which black plays an extremely early f6 pawn push
IM Christoph Wisnewski suggests this line for black in his book on the Nimzowitsch. I think it's just as interesting (and sound) as the 3...Bf5 main line.

As I’ve begun adopting the Nimzowitsch Defense as my main defense against e4 by white, I’ve discovered a very interesting line in the Scandinavian variation in which black plays an extremely early f6 pawn push
IM Christoph Wisnewski suggests this line for black in his book on the Nimzowitsch. I think it's just as interesting (and sound) as the 3...Bf5 main line.
I agree. At worst, you transpose to the mainline. At best, White starts thinking earlier in the game while you as Black are still in prep.
As I’ve begun adopting the Nimzowitsch Defense as my main defense against e4 by white, I’ve discovered a very interesting line in the Scandinavian variation in which black plays an extremely early f6 pawn push
It seems black intends to play fxe5 to try and get the knight onto f6 but this can be prevented with f4 or Bb5 (preventing Nxe5 after white recaptures on e5). Perhaps black intends to play e6 Ne7 g6 Bg7 and then O-O taking advantage of the semi-open file after an eventual fxe5? If anyone has any knowledge of this line and how it’s intended to be played I would really like to know.