there is exactly one and it experiences everything that is possible to experience simultaneously.
I would not use the word "experience" since for this state of existence, there is only mind and anything that could be described by experiences are actually perception. The Mind, the only mind, perceives its thought in the moment, not over time. But does it experience those thoughts? This is an epistemological argument. Since we can't truly know the phenomenalogical nature of what our sense tell us, we can't even know our senses, only the perception they feed us, thus, the only thing that exists is this one moment of perception that we exist in this world.
What about 7 billion people on Earth but actually they're all one
There are no 7 billion people, there is only the perception of the information about 7 billion people. One can't even know the person in front of them is real, let alone 7 billion people you can't possibly meet.
Solipsism takes the position, the one mind is my mind, and yes, that is my position, everything, EVERYTHING exists because I exist, but I also take the position that I am not important. I'm not the Red King snoring away at the base of a tree dreaming Alice. I'm dreaming myself and all those experiences. I am nothing more than a "crystalline thought in the minds of God," but so is God, and there is only one thought.
I, just last night, learned about Baruch Spinoza. He argued that God and Nature are one and the same, and that man, as part of Nature, are also one in the same with God. This is the one mind view, as well.
His views on Ethics (I have to read up more about him) appear to dismiss the idea of Good and Evil and lean towards harmony and artificial constructs based on position, or perspective.
The metaphysics of the Universe consist of substance and mode. There is only one substance. It is from and of itself. There are an infinite number of modes that cause the substance to appear divided. Modes, need substance to exist. They are attributes or relationships that don't exist on their own.
This is like matter and energy. Matter appears to exist from and of itself, but energy is a consequence of matter and its relationship to matter. It seems Baruch Spinoza also argued that since there was no power that could prevent God from existing, God (The entire Universe) must exist.
Spinoza was excommucated from the Danish Jewish church for his ideas.
-Will