Typical firing patterns of (some) motor neurons
I can't answer the whole question, but what I do know:
An actionpotential can't have a small amplitude, the amplitude is always the same. If a neuron gets excited enough there will be an action potential, otherwise there won't.

"When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire...for any given neuron, the size of the action potential is always the same. " 
quoted from https://faculty.washington.edu/chudler/ap.html

Neurons have a maximum firing rate, a point where they cannot fire faster. (http://blog.eyewire.org/why-do-neurons-fire-at-a-maximum-of-about-200-hz/)
So to move faster your body can't fire faster. But it can fire more: more neurons fire if you want to move faster, and less neurons fire if you want to move slower: https://blogs.scientificamerican.com/scicurious-brain/when-you-run-fast-your-brain-runs-faster/

I do think your first row of spikes is kinda correct. Neurons fire as long as you move your hand/finger(s) in a certain direction, and as soon as these neurons stop firing and their complementairy neurons start firing you move your hand to the opposite direction.