That is easy from Christian doctrine. God does not need us, not even for fellowship or to express love. That is one of the significant facts of the Trinity. Three persons in relationship and fellowship with one another. God is fully self-sufficient. He creates not because he must, but because can and he loves too do so.
Then there is your second point:
I think you are right!
In fact, he loves creating so much that the idea of many prior epochs and eras seems wholly consistent with him and his character. I like how the theologian Tim Saleska puts it,
I think of God as a poet or an artist. Perhaps God’s work of creation is like that of an artist creating something beautiful, rather than a lawyer trying to make a case for His existence. If so, the question is beside the point; akin to asking why would a poet put archaisms in her poem (and then not leave evidence that they are archaisms)?
Then, quoting Terry Eagleton with some theology worth carefully reading to understand.
God the Creator is not a celestial engineer at work on a superbly rational design that will impress his research grant body no end, but an artist, and an aesthete to boot, who made the world with no functional end in view but simply for the love and delight of it. Or, as one might say in more theological language, for the hell of it. He made it as gift, superfluity, and gratuitous gesture–out of nothing, rather than out of grim necessity. In fact, for Christian theology there is no necessity to the world at all . . . . He created it out of love, not need. There was nothing in it for him. The Creation is the original ‘acte gratuit.’1 The doctrine that the world was made out of nothing is meant to alert us to the mind-blowing contingency of the cosmos–the fact that like a modernist work of art it might just as well never have happened, and like most thoughtful men and women is perpetually overshadowed by the possibility of its own nonexistence.
So that is my answer to #4. This scenario of prior eras of life makes immense sense of an old earth. God created the world, and he created all sorts of life, for the joy of it. He was not content to leave it empty, like a blank canvas, for billions of years. He filled it with life of many kinds, wiping the canvas clear again at times, until He made us, the ones to whom was granted the gift of the Incarnation.