Teaching and writing about philosophy is about the only thing I've ever been really good at.

There is no author or legislator of the moral law. It is simply valid in itself in the nature or essence of things. We become autonomous only when we obey it, because then our will aligns itself with the objectively valid law, and our choice follows the same law as that we give ourselves. We can think of rational faculty (or the idea - the pure rational concept, not exhibitable in experience) as the legislator or author of the law because reason recognizes an objective standard, and to that extent is already aligned with objective moral truth.

As I understand it, Kantian constructivism is partly a position in normative ethics and partly a position in metaethics. In metaethics, it is the position that ethical claims have truth values, but their truth conditions consist not in a set of objective facts to which they correspond, but instead in the outcome of some procedure of deliberation resulting in decisions about what to do.

There is a very common, though also very silly, picture of Kant according to which as empirical beings we are not free at all, and we are free only as noumenal jellyfish floating about in an intelligible sea above the heavens, outside any context in which our supposedly "free" choices could have any conceivable human meaning or significance. Part of the problem here is that Kant faces up honestly to the fact that how freedom is possible is a deep philosophical problem to which there is no solution we can rationally comprehend.

I think the term "Kantian constructivism" as an oxymoron. Kant was a constructivist about mathematics, but not about ethics.

Smith could not be expected to have anticipated the horrors that were to come. But even in his own time, he was a defender of certain state actions that he thought necessary in order to safeguard the good effects of commercial society (Smith did not speak of 'capitalism' and was acquainted only with an early undeveloped form of it). Among these state actions the chief was general public education.

Kant does represents a distinctively modern view of the human condition in contrast to that of ancient high culture, found in ancient Greek ethics and also in ancient Chinese ethics.