I don't see why you restrict yourself to Plato's philosophy. Any reason?
No reason other than I like it.
I'm not entirely sure how you mean it but why would matter have any inherent qualities, i.e. have qualities before the god could decide on the specifics of the universe he's going to create? Why would an almighty god found himself somehow restricted in his choices by mere matter. Cannot matter and its properties be entirely his creation?
Obviously God in this scenario either isn't all powerful or, just as bad, erred in using faulty material. Ex nihilo is a Christian invention AFAIK. In the Platonic universe, the order or intelligibility of creation is the divine creation, not the matter. The potential ie raw material existing formless or chaotic was preexisting.
Also, I'm not sure why you think the god would be prevented from achieving the perfection of the idea. It is assumed in the OP that the god wanted to create a complex universe with man in it and for man to have free will. What idea gets to remain imperfectly implemented here?
EB
I would say the universe isn't perfect. Maybe I'm wrong and God is right, but if this is a perfect universe, I can't see it.
Seems to be an attempt to reconcile the idea of perfection with the limitations we all know exist. The Gnostics pose a corrupt creator God(which explains a lot). In Christianity, suffering is central but still the imperfection manifests itself in injustice.
From Timaeus
Let me tell you then why the creator made this world of generation. He was good, and the good can never have any jealousy of anything. And being free from jealousy, he desired that all things should be as like himself as they could be. This is in the truest sense the origin of creation and of the world, as we shall do well in believing on the testimony of wise men: God desired that all things should be good and nothing bad, so far as this was attainable.
Anyway, all of these stories are really about one thing: the emergence of consciousness and the problems that that emergence entails.