I think if there were to be a solution to the problem of free will, it would have to be a compatibilist one. Unfortunately, from that it does not follow that there is such a solution. Many philosophers find this an unwelcome message, and as often happens in philosophy, they punish the messenger by ascribing to him an entirely imaginary but untenable position.

Kant's treatments of rational theology and metaphysics were aimed primarily at theoretical questions. His attitude toward the pseudo-sciences of "special metaphysics" in Wolff and Baumgarten was always double-edged. He did see them as pseudo-sciences but also valued their doctrinal value and especially their regulative value for the empirical sciences. Like his views about religion, I don't think any of this is any longer viable in its original form.

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.

Freedom is an unprovable but unavoidable presupposition, not an article of faith.

Kant's aim was to develop a religion within the boundaries of mere reason (that is, reason unaided by special empirical revelation) and then to ask about existing ecclesiastical faith (especially about Christianity, and the Lutheran Christianity of his time and place) how this revealed faith must be interpreted if it is to be reconciled with reason, and even seen as a wider (though morally optional) extension of a religion of reason.

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

Kant does not think there is anything wrong with being beneficent from sympathy. He thinks we have a duty to cultivate sympathetic feelings by participating in the situations of others and acquiring an understanding of them. He thinks we also have a duty to make ourselves into the kind of person for whom the recognition that something is our duty would be a sufficient incentive to do it (if no other incentives were available to us). That's what he means by "the duty to act from the motive of duty".