Thank you for your question, it is an important one for everyone, but is difficult to find an exact answer. Because, like you say, we cannot fully comprehend God or His nature, so, we must look for examples we can relate to. Example: in a court of law you present evidence to try to show the argument is true beyond a “reasonable doubt”.
We have evidence through natural sources and through super natural sources. Eye witness accounts, and Holy Spirit inspired accounts. And these are recorded in God Holy Word, the Bible. Science shows us proof for a designer and the Bible tells us who that designer is. All of your questions cannot be fully answered, but what we cannot fully comprehend we can apprehend enough to “be sure beyond a reasonable doubt”.
God is a being that “exist in relation”. God the Father, God the Son, God the Holy Spirit, three "Who and one “What”. In His essence He is, they are, in a loving relation, all equally the same, all equally sepperant. God is Love by His nature: hence, we were not created that He would have someone to love, as if He were cosmically lonely, His essence is love. This not in anyway complete, but because of space, it is a place to start.
Nature of God:
Because of what we can apprehend about God through the Trinity, and Jesus being part of that loving essence, we can find good reason for Gods nature. But first lets look at an example of the Trinity that we can get our heads around a little bit.
1st Marriage: The Bible tells us that when a man and a women marry they become one “Flesh” no longer two but one. They are “one in what” , but still “two in who”. One in their essence, before God, but two in their persons. They are now “in relation”, a loving relationship at the core. (in a perfect world)
2nd Christ: Jesus is, God in human form, the expression of God essence (nature), His way to show us His character as recorded by eye witnesses and divine revelation. So, a study of Christ shows us Gods nature.
Yes, the nature of God and the person of God are incomprehensible, but through study and the revelation of the Holy Spirit we can apprehend it “within a reasonable doubt”. This is a truth that is held in tension, but you can find a peace within it, and it is very rewarding when reached. Keep exploring it and Gods Holy Spirit will guide you to an understanding that you can share with others. God bless you…
(remember this is just the tip of this subject)