I am currently reading Chess Openings: Theory and Practice - I.A Horowitz. The first opening displayed in the book is a variation of the bishops opening: 1. e4 e5 2. Bc4 Nf6 3. d4 exd4 4. Nf3. Seemingly the best continuation for black, if they can defend properly, is to continue 4 ... Nxe4 and to 5. Qxd4 respond with 5 ... Nf6.
From this point Horowitz goes on to consider the variation 6. Bg5 Be7 7. Nc3 c6:
rnbqk2r/pp1pbppp/2p2n2/6B1/2BQ4/2N2N2/PPP2PPP/R3K2R w KQkq - 0 8
This seems fine for white (to me) by basic chess principles (good development, castling around the corner). However I have two questions:
What if black had responded with 6 ... Qe7+? It seems like white either trade queens and is worse or moves the king allowing Nc6 and is just worse?
What can white do after 5 ... Nf6? My thinking is that 6. Bg5 is the mistake so perhaps 6. Nc3.