You can determine the net work done on an object two ways.

1) Calculate it's change in kinetic energy:
$$W_{net}=\Delta K$$  

2) Directly add up the work done by all forces on the object. 
$$W_{net}=\sum_i\int \mathbf F_i\cdot\text d \mathbf x$$

In your case, we only have one force acting on each of our objects, and it is conservative. Therefore, we can also use the fact that the work done on an object is equal to the negative of its change in potential energy
$$W_{cons}=-\Delta U$$

It seems like your points 3-5 is trying to get you to say that only one of these three is the "right way" to find the work done on an object, when in reality all three are equivalent and equally valid. 

Another point to be made. The work done does not depend on the speed of the object alone. It depends on the kinetic energy, which depends on the mass of the object in addition to its speed. A more massive object moving slowly can have the same kinetic energy as a less massive object moving fast.

Similarly, the work done by a force does not depend on the magnitude of the force alone. It depends on the distance over which the force acts as well. A large force acting over a small distance can perform the same amount of work as a small force acting over a large distance.

With all of that being said, your question seems to have some areas where it could be more specific.