We will. Football is a simple game and if the basics are all covered and executed well this will mean any negative variables, and there could be many, have much less chance of affecting the outcome of the match.
The opposition midfield can't just move into any gap if they are being marked properly and pressed when they receive the ball. Obviously the defence moves out but that's not too defend deep. That's a basic one too. The keeper needs to be aware of any balls over the top and play the sweeper role.
No you're wrong. The attack begins the press and the midfield presses only when the opposition midfield get the ball, if they get the ball. Defence too. The whole point of the high press is the press the opposition immediately they get the ball. It doesn't mean that all the midfielders join the strikers in pressing the defence and then leave massive gaps.