Well, technically there are some requirement for consistency, but they mostly boil down to a simple structure. As long as you are able to rank any two experiences relative to each other, the rest is sorted out by transitivity. The exact number of the utility score is not important, any order preserving transformation of the scale is equivalent for the choice/ranking. The question is therefore simply: can you choose between them? And indifference is allowed.

Multi-faceted experiences make such comparisons more difficult, for pretty much the same reason that comparing between experiences of different persons is difficult. There is not that big a conceptual difference between 'better in aspect A (food) but worse in B (pop song)' and 'better for person A (me) but worse for person B (you)'. The one thing I find so much harder about the interpersonal setting, there is no single actor to make the decision, while we can rely on the single actor to make the choice (even if it is indifference) in the multi-criterion setting.

I think the term you are looking for is indifference, it's like a zero on the scale between suffering and joy, not really a problem. Interpersonal comparisons, or how to value my joy relative to yours....

You have a typo there, the end should be Q.E.D.

But then both utility and (the experience of) freedom are subjective. The most important difference in your reasoning seems to be that utility is individual, while your construct of freedom takes others into account. So, swapping utility for welfare with a sufficient 'welfare punishment' for crimes against others, would lead to the same outcomes: Killing is bad, don't hurt the utility of others, and do what you like otherwise.

But then both utility and (the experience of) freedom are subjective. The most important difference in your reasoning seems to be that utility is individual, while your construct of freedom takes others into account. So, swapping utility for welfare with a sufficient 'welfare punishment' for crimes against others, would lead to the same outcomes: Killing is bad, don't hurt the utility of others, and do what you like otherwise.

It's quite unlikely they smell insuline levels, they probably smell sugar. If your blood glucose goes up your metabolism changes, cells start burning more sugar, your kidneys start flushing out sugar, probably your skin too. So there are a bunch of potential chemical clues there.