Your synthesis of Luke and Tobit is definitely an improvement on Luke and Tobit on their own. The Golden Rule I was brought up on always seemed inspiring like you say, and also, like Tobit, although not quite as not as much as Tobit, as you say, is very immediate -- referring to it, you relatively instantly know how to act.

I recall Kant believed his version, the Categorical Imperative, was self-evidently true. I interpreted this to mean that reason shows us all humans are equally valuable, which to me is the source of morality. I think (?) Kant said humans are ends in themselves, and should not be treated as means to another end.

This sounds to me like a more sophisticated way of articulating the essence of the imperative, the one that most closely follows from the idea of human equality, although of course much less immediate.

I'd think the most sophisticated articulation, based on the other maxims, is "decide on an individual basis." This opens up thinking about what will be best for the other person. Usually this will mean what pleases them (just as we all want to be pleased).

I'd see "best" as that which supports their own ends -- their deepest ends, not necessarily their in-the-moment ends.

Of course, to discern their deepest ends takes effort and wisdom. Before that is accomplished, one should act cautiously, assuming no more than necessary, generalizing over what most people's ends are. This brings us back to the synthesis you propose.