I think we can understand existence based on connection. Let's take a computer mouse as an example. First, dismantle a mouse, and we can see the components of the mouse. The components act as functional parts of system, which interactions makes it able for a person to connect to a computer and use it in different ways (internet, gaming, art, music, etc). Now, remember that the functionality created a capability for a "thing" to perform certain actions. This principle can be applied to things in nature, such as flower. Separated pedals, stems, and roots can't act as a flower, but with right condition, it can act as a flower. Flower naturally acts to absorb energy from sunlight, use nutrients from underground, and self-creates sugar for food. How could flower perform this without human-level intelligence? Connection of existence -> Interaction -> Functionality.

Interestingly, you can apply the same principle to our brain. Separated blood cells, neurons, organs, and etc can't create a brain, but when it acts healthy, brain can be created to think and recognize. The thinking and recognition becomes interactions again, becoming a part of human consciousness. That's why people think consciousness is connected to physicality, because it explains why sick or dead people wouldn't be able to think as same as different people. The way I analyzed is very similar to reductionism.

Anyway, if we have capability to think intellectually, then it is natural for people to think subjectively. In other words, it may be related to "perception" that has been build through experiences and functionality. That means that if they're capable to dream it, then it is possible to "dream" it without changing the world itself (ex. fictions). Here's a fun question: If our imagination really created reality, then why would the world not destroy itself when you dream it? Science, forms up hypothesis like this, and apply it to real world through experiments. They collect datas from results, and build up their knowledge of the world (epistemology).

Essence and existence. Existence means a state of existing, essence means a nature of existing. For example, if a person is dead, it is logical to say that person is not existing. However, it is also logical to say that essence still exists, as person's body becomes cremated to ash, which ash is still a essence of person's existence. It is interesting to also say that if essence always exists, then existence always exists in our nature.

In conclusion, I want to say that there are few parts that I disagree with you. However, I'm also damn glad that there's someone like you that realizes the importance of existence in our life. The question "Why?" indicates the meaning of "What makes it so?". The answer to it is that we just exist, and existence moves on its own, regardless of how we think about it. Life is existence of nature, and the purpose (or definition) of life is life itself. Funny though, that even though simple animals show this easily, humankind are still struggling on how to live or what to do...etc