Kant is not saying - about freedom or any other subject - anything of the form: "Not-p but we must assume that p." That's close to self-contradictory, like Moore's paradox: "p, but I don't believe that p".

There is a lot in Adam Smith that reflects the insights of Rousseau and anticipates those of Marx.

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.

I think Fichte did take it further than Kant by arguing that we can regard the moral law as objectively valid only by seeing it as addressed to us by another being, even though Fichte thought God could not literally be a person who could address us.

If we decide rightly what to do, or use a correct procedure for making such decisions, that has to be because the decisions or the procedure rest on good reasons, and these reasons consist in the apprehension of truths about what we ought to do. Because these truths must constitute reasons for our decisions, and because in the rational order, reasons must always precede the decisions based on them, the truth conditions of claims about what we ought to cannot be reduced to, or constructed out of, decisions about what to do, or procedures for making such decisions.

Kant takes a free will to be a being or substance with the power to cause a state of the world (or a whole series of such states) spontaneously or from itself.

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.