On 1&2 could you provide a bit of context on what you are responding to.
On #3 the incident meter provides a scientifically objective reference point that we regularly refer to as middle gray from the scene. The testing for the film has already been done, its simply the ISO speed. If our tools are working correctly and we are reasonably capable in processing our films, then our results will be very close to ISO standard and mid tones will fall nicely on the paper with reasonable shadow and highlight detail.
There are several wild cards here. Our skills and understanding are the biggest factors. The other big one is creative choice.
Testing is valuable in refining our skills, understanding, and creative vision but the baseline is already there.