Kant's system of duties constitutes a Doctrine of Virtue because the duties also indicate what kinds of attitudes, dispositions and feelings are morally virtuous or vicious.

Fichte takes an I or free will to be not a thing or being but an act which is not undetermined but self-determined, in accordance with reasons or norms rationally self-given.

What is central to morality is rational self-constraint (acting from duty), in cease where there is no other incentive to do your duty except that the moral law commands it.

People who enjoy the privileges of success must use these privileges to benefit those who do not have them. These privileges constitute a deep hole they need to climb out of if they are to prevent its being the case that the world would have been better off if they had never been born.

Kant regards the universalizability test for maxims as focused on a very special sort of situation: one where the agent is tempted to make an exception to a recognized duty out of self-preference. The universalizability test is supposed help the agent to see, in a particular case of moral judgment, that self-preference is not a satisfactory reason for exempting yourself from a duty you recognize. Kant thinks, as a matter of human nature, that this situation arises often enough and that we need a canon of judgment to guard against it.

In my view, there was a long period in which analytical philosophy had little to say about ethics. I think their intellectual tools did not do well with it, and analytical philosophy was above all about revolutionizing the philosophical tool box. It was more or less assumed that the Truth about ethics was some form of utilitarianism (perhaps because some consequentialist calculus looked to them like a respectable tool). Kantian ethics was then interpreted as a particularly odious version of the False - "deontology" - and treated with contempt.

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