Should the engineers be able to build obstacles?

[Dog Soldier]

Because entering a minefield does not require 100% of movement troops for that turn.

Neither does Obstacles. OBSTACLES do. All one has to do to negate an OBSTACLE hex is move an single, small unit into the hex with the OBSTACLE. Then the hex is considered penetrated and reduced to Obstacle. All units moving through the hex after that pay a minimal movement penalty.

I see very little to gain. I can see OBSTACLES appearing all over the place, far more than ever were there to affect the historical battle. VM makes real good points about how this will need more thought.

Dog Soldier