Circle means nothingness because is the potential: everything can happen, averything can be. Is the recipient were light can be received. How can someone receive if their recipient is already full? The circle symbolize the idea of the continous flow of giving and receiving, that is why the circle is everything and nothing at the same time. Some of this concept comes from Kabalah.
For perfection, it exist in authenticity. Perfection is not "being technically or socially correct" being very clean and neat, or exactly following some academic rules. Actually imperfect things don't exist. As I see it, imperfection is the true illusion, as things are just the way they are, and the way they are is the best way they could have been. Perfection is in authenticity, when the things you do are inspired by your true spirit. When you let your inner self talk, then there is perfection, despite the mistakes.

By the way, there are no mistakes, there are no bad colors, there are no wrong musical notes, all of this are judgements of our mind, our ego, that says something is or not perfect. The aeternal perfectibility of Rousseau doesn't mean we need to seek to be perfect, it means we need to seek to be a better version of ourselves each day.