It seems that Black ought to leave the pawn altogether alone: 3...c6! 4.dxc6 Nxc6 5.e3 e5!? There are other 5th moves Black could try ...e6, ...g6, or ...Bg4 that seem OK as well.

The common theory here changes so much that it really just comes down to personal preference, knowledge, and preparation.

possibly your opponent is aiming to slide into an Alekhine Defense type position?? not necessarily a good idea

Joe, Charlie just means that this is worse, that's all.

5..g6 would have been bad, but better than the text. But how about 5...e5!?

I think in this position 5....e5 just loses a pawn, but with the N on f6 rather than b6, it equalises, because if 6. dxe5 Qxd1! and if white recaptures with the Nc3 then Black regains the pawn with Nxe4 and if white recaptures with the king then Ng4 forks the pawns at e5 and f2.

It looks quite hard to develop Black's game in any meaningful way. With 5...e5, Black would, one way or another, have been threatening to simplify the game. Queens are very likely to have disappeared shortly, which would have minimised the awkwardness of Black's position.

I was thinking black should be aiming for c7-c5 at some point, so maybe Nb-d7 to prepare it?

7...0-0 or, why not strike at the centre by 7...f5!?

Long castling is very aggressive, and a bit risky, here, as well. The King's position is not very secure, and, assuming he wants to attack on the K-side, White's army on that side of the board are still sleeping in their barracks!

His Be7 is his good bishop, defending his weak dark squares - in particular d6.

black's position is passive, and passive play is usually dangerous for the passive player, but not always

I would have been very reluctant to weaken my K-side in this way. Other than castling, I might have been inclined to put the frighteners on and play 10...a5.