How can God choose what not to know without first knowing it in order to make the choice?
I think its more about the ability to know. Like having the key to someone's hotel room, but choosing not to use it to see whats happening inside the room.
Where does the Bible say Adam and Eve were created perfect?
Its more or less concluded from Paul's passages in Romans Chapter 5, where he states how sin entered the world through Adam's disobedience and death through it, and how Jesus' act of justification can mean everlasting life for all. This alludes to the point that there was a time when there was no sin, (means perfection - relative, not absolute) and hence no death.