must be enough, and also required.
white has two unavoidable captures coming up: on white's next move, the
light square bishop will go to either b5 or c4, both of which force an unavoidable trade on the next move.
Black can prevent only one of those moves, so
on move three
the first objective is completed.
Continuing from there, white will play
next. It threatens black's F-pawn, and also the queen's rook or some other piece in front of it. All those pieces cannot possibly dodge, so the only ways to stop the queen from capturing are:
- Some piece steps in between, in which case it will be the one to drop
- Black takes white's queen with some piece, in which case the g-pawn that was protecting the queen will finish the job.
During all this, there's always the possibility of black giving check in an attempt to slow white down. However, every square from which the white king can be checked is guarded by a white piece, so taking the piece that's giving the check will bring white's plan back on track.
The exception is a knight giving check from g2 or c2. These require a bit of cleverness on white's part: a knight can only reach g2 on move 4, when it's protected again, so that square is not a problem. But if black starts with 1. - Nc6, aiming eventually at 4. - Nxc2+!, then white needs to thwart black's plan with
1. e3 Nc6
which stops the knight's advance. Since every capture with the queen always comes with a threat of completing the objective on the next move, white still has ample time to bring the light square bishop into the game.
I hope that finally covers everything..
To see why this cannot be improved, it's enough to see that
From the staring position, there is no way for white to reach rank 7 with any 2 moves.
Since black will not help, bringing any two pieces to where the black pieces are cannot be done any faster.