I play fewer 1. e4 games these days but dabble occasionally.

I know my opponent quite well. In real life his OTB grade is considerably lower than mine. When he is in the groove he will play stronger at correspondence chess because he will analyse a position for long periods with incessant clicking of the analyse board and then allows his reply to "mature" for a day or two before sending it. Lately he has become more slapdash.

This is the start position of the four knights opening. Regarded by theorists as pretty much played out. From my point of view it gives a straightforward route to a playable middle game, without being cramped.

I think this is the best move here, but Bb5 and g3 are common enough.

4...Bb4 is also playable.

5. Nd5 is the Belgrade Gambit, but I don't know much more about it than the name.

Here I believe the book move is 7.Bd3. I saw no reason to follow theory any further. The queen threatens the bishop, has the possibility of going to e5 with check disrupting castling and looking at c7, and could, in combination with Bg5, pressure the f6 knight. Also in the event of 7...Bxc3 then 8. Qxc3 Nxe4 9. Qxg7 looked like a game.

The only move to harass the early developed queen, but I don't believe it achieves much, although black can argue that Bb7 is a threat.

c7 is safe for the moment as e4 is vulnerable.

White prevents his c pawns from being doubled because if Bxc3 Bxc3 Nxe4 then Bxg7. The Bishop on f1 holds g2 after Rg8 in these lines.