What would the best move be in this situation ? (black turn to move)

no u

Most people here play e5 - you'll get a strong pawn centre and pawn chain after the knight moves, gaining two tempos. Make sure to play d4 and not e4 though, because that would allow the knight to go back to d4 where it is very active and unthreatened.

Bb4 although seemingly great is terrible because Qa4+ eventually wins at least a pawn (after 6..Nc6 7. Nxc6 Bxc3+ 8. bxc3 bxc6 9. Qxc6+), and shatters your queenside. Since you haven't developed any kingside pieces that is troublesome.

Nf6 I believe intends to recapture with the knight but Bg5 seems like something to worry about.

My personal preference probably goes out to Bc5 followed by Nf6 to guarantee myself a safety option with castling whenever I get the time to do so. The position is mostly opened up and therefore targeted at the queenside so it's a great way to check off king safety from your list and focus on tactics. I guess the difference here is that when playing Nf6 like I said earlier the intent is to recapture on d5. Probably I'm just worried of Bg5 in this position that I prefer to play a different move order.

It's Black's move.

I think e5 is best.

Bishop b4 ?

You're looking at the board from Black's perspective. You probably meant this:

Pin with Bb4, if a3 then Ba5. But after Bb4 then Qa4 with check wins at least a pawn like I described in my post.

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Stop.

Nc3