Here's my take on the problem of evil and suffering, free will, and Heaven...
Or rather the first question is, is human intelligence unlimited? Or is human intelligence limited and may possibly be unable to understand God's plan/intention completely.
God's ultimate purpose is to build an eternity called heaven. He's working towards this goal. Not as you said in OP that His purpose is to reward humans on earth. Heaven is not the reward, it is the purpose He's working towards.
However, out of human arrogance, humans usually assume that today's humans are God's whole purpose and heaven becomes a less important place for the reward of men on earth.
That said, planet earth is a place outside God's realm. This is so ever since Adam was kicked out of Eden. Eden on the other hand is a godly place, not earth.
Once it is outside God's realm, earth becomes a wilderness full of wolves. It's naturally so. Any place outside God's realm is naturally a place where evil grows freely. Wolves and beasts are supposed to be everywhere. Earth is already a better place. It is so because God still has a job to do on earth. Earth is still a better place then hell because God still cares.
Now what does He care? His sheep are still among the wolves in the wilderness. That's why.
Planet earth thus is a place described as,
1) a wilderness full of wolves (including beasts like Satan), mixed together with God's lost sheep
2) a crop field of God where in the end some souls will come out as God's harvest
3) a large filter to sift out the unqualified for God a get His wheat as His products
4) a field where weeds grows with wheat. Once they can be told apart, God will get the wheat and burn the weeds
I think that if you can read the Bible more wisely, you may figure out all the answers to those questions in OP. People don't get the answers because human intelligence is the biggest issue of the arrogant humans themselves, without their own self awareness.