Without free will, true worship cannot exist. (If God is God, he certainly has the right to create us for the sole purpose of worshipping him.)
To your latter points, I agree that we know clearly what evil (a.k.a sin) is—sin is anything apart from God's character (e.g. the fruit of the spirit to start).
However, it's not up to us to "get rid" of evil, that's on God, and that's exactly what he did when he sent his son Jesus to die on the cross as a substitute for the punishment we deserve, and when he rose from the grave he signified that substitution was complete. If we truly accept that fact, then God considers us saved ("redeemed"). And, one day Jesus will come back and eliminate evil once and for all.
As to why God allowed evil to enter the world in the first place, well, that's one of the cornerstone discussions of Christian theology, I can't easily summarize that here. In short, a redeemed world can know God's love and worship him more deeply than a world which was never fallen to begin with. (And again, if God is God, he absolutely has the right to create us—and all of creation—for the sole purpose of bringing him glory.) Here's an excellent article that explains this more fully.
I had to go into a partial psych care program because I literally was only eating like 1 meal a day, I was very underweight, and it was making the depression really bad because my body had nothing to work with. Even when the ADHD med wore off I had so little energy that I didn't want to find food before bed. The psychiatrist ended up switching me from Vyvanse back to Adderall, and then a month later lowering my dosage of Adderall from 30mg to 20mg. I definitely feel like my ADHD is harder to manage, but it seems to be the happiest medium I've found for the moment.