JMAN300Sd, I will try to address specifics to your inquiries.

You are a sort of test horse here as well.

Yes the voltage will change on numbers 3,4,&5 as you adjust the elements on 1&2.
That is to be expected and is the reason you want an extra set of hands there to monitor one voltage and then quickly check another as you move the element.
With the hunting stabilized to zero with the small circuit I mentioned it will be a lot easier for you.

What you refer as the floating will remain to some extent and is normal, it becomes much less of an issue with the hunting eliminated.

As you get closer and closer to the final position the floating as you describe will lessen.
The floating and hunting are separate things.
The floating is being caused by engine parameters being changed in some way by your application and is normal in my opinion.

.