We can treat human responses to cognitions as involving law-like connections grounded on free choices which show themselves in our character.

The relation of the law to the self is only a helpful way of thinking about the law, that helps us better understand its validity for us.

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

Kant's description of most ethical duties reads more like a description of moral virtues and vices. Once we see this, we see that Kantian ethics is indeed a kind of virtue ethics, and that it does not "divide the heart from the head" (to anticipate one of your later questions) but instead recognizes the deep truth that reason and emotion are not opposites.

We can never prove that we are free or integrate our freedom in any way into our objective conception of the causal order of nature.

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

I don't think Kant's theory looks bad to people except insofar as they have misunderstood it (for instance, as heartless and ironheaded, or as committed to an absurd metaphysical conception of freedom that violates Kant's own philosophy).