As a Christian (Catholic) I have to say that I love my religion and accept it beyond a shadow of a doubt, but I can see how someone looking in could have quite a few questions. First thing's first, if you can't accept the Christian God for what he is, then you're paddeling up the wrong river. The first commandment says it best "I am the Lord, your God, you shall have no other gods before Me... you shall not make yourself a graven image of any likeness". Essentially people have made gods to suit themselves for eons and God has revealed what he's like through the Bible. As with any other relationship, if you can't accept Him for who He is, then maybe it wasn't meant to be.
Wen you say that he's one but split in many ways, St. Patrick made the best analogy of using a clover to describe Him by saying that the Father, Son and Holy Spirit are one in the same, but each aspect of him is still uniquely different and apart from the rest.
An eye for an eye, tooth for a tooth is from the old testament and was basically turned around by Jesus when he says 'when someone slaps you on the left cheek, turn to him your right' and it was him teaching about forgiveness. As Christians, we follow what Jesus has taught us. That being said, I don't mean to say that we should completely ignore the teachings of the old testament but put more focus on Jesus' teachings.
Finally, as for Adam and Eve, I don't know that much about DNA and how long it takes for the gene pool to mix and change, but I'm sure that after thousands of years of marriage between one clan and another that there would be a mix of various DNA with stronger and weaker characteristics that appear over time.