3. God put Lucifer in the Garden to perform some kind of task. He was the "anointed cherub that covereth," and wore some type of elaborate outfit made of very precious gems. Coupling that with what his name means - (bearer of light; or bright star), and it's possible that his job was to tend to the Tree of Knowledge and to show (light?) the way for the other angels to this tree.
4. That tree bore fruit, not for Adam and Eve, but for the angels.
5. I don't understand this question. God parading the animals past Adam, who gave them their specific names, generated in Adam the realization that he was alone.
6. A couple of theories come to mind here: a) God knew they were going to fall, so He "prepped" them by having them get used to this "needless activity." b) God created them to live in both states (glorified and fallen), knowing they were going to eventually lose their glorified state. In other words --- Plan B requires eating to stay alive, Plan A didn't. So when God told Adam, "to you it shall be for meat" in Genesis 1:29, that statement carried a hint of prophecy in it.