Kant 10/15

My main question for Kant can actually be split into two; 1) why MUST we assume the existence of a god, and can we know his/her/its characteristics? And 2) if this assumption were tossed out, how would your system change?

If the God-assumption were abandoned, the conclusions he drew from the freedom principle would be quite different; his position on suicide would be nullified to some extent (some points could still be debated), and “defiling oneself by lust” would become a matter of pure opinion.

Also, how would the claim that the only true knowledge is a priori knowledge be justified? This is something I just can’t see…