First, the coefficient of friction is unitless, so , not 0.20 N.

You are over thinking this one. The static friction force is only as large as it needs to be to keep the object in place. So if there is no horizontal force applied, .

The maximum possible static friction force between the box and the surface will be:

Since the applied force of 7 N is less than this then, yes, the static friction force will be 7 N.

Since the maximum possible static friction force is 12 N, then any applied (horizontal) force greater than this will make the box move. So yes.

Yes. Briefly, this comes from the fact that, once the box is moving, the sum of the forces in the horizontal direction must be 0 N to make the velocity constant.

This applied force is greater than the static friction force of 12 N, so the box will be moving. Since it is moving the friction is kinetic, which has a constant value. So

-Dan