Question 1: Yeshayahu 45:7 describes the fact that God created rah. Bereshit 1:31 tells us that God did watch all that he had made and saw that it was tov me’od. If something like rah is created and one of the components of that which is called tov me’od then.. What is rah good for? (why was it created in the first place?) Question 2: Why was it forbidden to take knowledge of rah if HaShem created rah; or created the tree of knowledge tov v’rah? Why wouldn’t HaShem allow the first human beings to take knowledge that which is tov and that which is of rah? (why else does this verse says: ’knowledge tov V’rah? - tov AND rah). Because from a human view it would seem that this knowledge/understanding could help us to do the good/right thing and refrain from doing the bad thing.
Everything in the world is good unless man, with his free will (which is also good), misuses it. Eating is good, but if you over-do it, you turn it into a yetzer-ra, a negative inclination. Same thing with sleep, sexual attraction or really everything is good, unless one takes it out of its proper proportion. This answers your second question as well, for tov and rah are one and the same topic, just whether it’s used or misused.