As to that most mystery-invoking of questions, "why?" . . . which I have myself long pondered and still even get a kick out of contemplating . . . .
First off I must say that for me . . . well, I already had a basic testimony of the existence of God, ever since I have pondered "why?" I knew He was there; His presence was obvious. My primary driving question then revolved around figuring out who He was and which of all the various "paths"/"religions" was THE truth to best reach and please Him. I didn't doubt He existed but I determined that there ought to be one way above all that He was best understood and related to which He intended the seeker to find and follow.
Right away, though, I too wondered and marveled at the "WHY?" of His being . . . and "why?" would He have ever created anything "more" than His complete, infinite self? . . . Especially, "why" would He make a universe and world such as this with all its chaos, violence, contention, confusion?
After much searching and finally coming to what I am now utterly convinced is "THE TRUTH" (Biblical Christianity) I must go to "His Word" to find whatever Authoritative answers are available. And indeed, one of the most helpful and profound values of the Bible (His Word) is that it gives us information about His character--Who He is, what He likes and doesn't like . . . so-to-speak, which helps immensely in reaching certain answers.
So, rather than come up with my own ideas of what I think God should be like, I can simply look into things He has had Written about Himself and His relationship to the world and humanity since the beginning of this creation. Clues are found there.
Because I already believe in Him and am totally convicted that He IS . . . and that He speaks to us through His Word . . . I am content to rely on whatever answers are there provided. Also, being "born again" I find that the Holy Spirit--Whose job it is to reveal truth--provides an ability to my mind and heart to See and comprehend things that my otherwise darkened mind would not be able to grasp. You should know that there IS a kind of supernatural wisdom that comes with "being saved" that is not really available before one is made a "new creature in Christ". . . .
Also, you should know that no amount of brilliant or satisfying "answers" will necessarily make it any easier to finally believe in and turn your life over to God. Jesus, when He was walking and talking among the people (and to the Pharisees, philosophers and lawyers, etc.) constantly gave astute and specific answers . . . along with His parables. Not only that, but He performed miracles that were witnessed by multitudes. But it did not matter to those with hard hearts and minds filled with pride; and it is commonly understood among believers that those who call themselves atheists or agnostics, who say that they would "believe" if God would just come down and show Himself to them and perform some miracle . . . that they won't, as we know that He DID already, and still they would not believe.
And not only "not believe" . . . but they went further to torture and kill Him!
The Bible teaches that the heart of man is "deceitful above all things, and desperately wicked" . . . and that in our fallen state we are natural, born rebels who hate God--even "children of the devil" (until we are born again)--who by our "unrighteousness suppress the truth." What does this last phrase mean? Elsewhere the Bible explains that every person is born with a deep-seated knowledge of God and of the truth, but that in our sinful condition, we suppress and hide that truth. Why? Because, as it began in the Garden, we have succumbed to the temptation to be our own gods. We do not want to answer to Anyone. We don't want there to be consequences to our life's decisions and our compelling love of self. . . .
Anyway, back to the question . . . "why?". . . .
Yet, again I must reiterate that . . . on the other side of Believing, coming from a position of non-belief or general agnosticism . . . NO answer will satisfy, no matter how correct, precise, astounding, and even if it did, another question would follow . . . and then another . . . and another ad infinitum . . . because the real issue is not so much about understanding with Reason and satisfied logic the "whys" or even "hows" of the situation . . . but, rather, the situation of a sinful, rebellious soul who rejects God and will continue to reject God regardless . . . until it realizes its awful condition and yearns to be free and at last desirous to submit and be saved from inevitable death and damnation. . . . That is what the Bible teaches primarily, as answer to most philosophic and/or mystical queries. . . .
As to "what want or need" . . . "a perfect and whole entity" might have to create a world and creatures, His Word teaches that He has no such "needs". You also implied (somewhat tongue-in-cheek I realize:) that He "suddenly felt the overwhelming compulsion to speak the universe into existence" which is also not the case. Nowhere in scripture does it say that He felt "compelled." He was not lonely and He has no needs, nor is He compelled to do whatsoever by anyone or anything.
Understanding God's attributes . . . personality . . . character . . . etc., does, nevertheless help somewhat the human mind appreciate possibly a bit of the "why" God may have decided to create.
For one thing, we are told "God is love." Perhaps, how better to express and share this wonderful quality of "love" than to create individuals with whom He can share a loving relationship? We are also informed that He is "holy", "merciful", "righteous", "just", "sovereign" . . . and obviously creative. . . .
As we are "made in His image" . . . although presently corrupted . . . we can kind of relate from our own experience. For instance, why do we create? There seems to be an inherent "joy" in creating . . . then expressing that creation . . . and sharing it with others. If we accept that "God IS" . . . and that He IS inherently creative--He just IS creative--then why wouldn't He simply create as a "natural" function of His very Being?
Above all, we are Told that the purpose of life--our lives--is to "glorify God" and that He made the "heavens" and such . . . to show His glory; and this is the answer that is most clear and satisfying to me.
Now, the carnal mind, fallen, which hates God and is in rebellion, of course, bridles at this. "Glorify God?" "What is He--an egomaniac!?" Then, the same mind flips God off and goes about glorifying itself!
But when I sit still and ponder . . . first off, that GOD IS . . . and that He is a Person . . . and that He is love . . . and righteous . . . and holy . . . and omnipotent, omniscient, omnipresent . . . eternal . . . unchanging . . . "no respecter of persons" . . . . And as I look at this incredible, detailed, sometimes quirky creation, from the miniature to the gargantuan . . . and realize that even all that I can see and somewhat comprehend, including the cosmos, He easily "holds in His hand" . . . then I am thrilled that He expresses/creates to show His "glory"--meaning . . . to just display and share what He is and can do . . . and especially to know that there will be no end to His doing this.
What we are witnessing and experiencing here in this world and the way it has gone . . . is to see what "life" is like when He is NOT recognized as the Sovereign; and how things go when created beings live and act for their own glory and self-serving purposes. It becomes a horrific mess! I expect there is no better nor more perfect way to show that difference and to portray the stark, alarming contrast between a creation which glorifies God versus one that glorifies and revels in its derivative self. . . .
So, He creates some entities . . . gives them a modicum and type of "free will" then watches as they immediately begin screwing things up thinking they know better. He allows the thing to run on for a time until it is so desperately wicked, confused and miserable that it is about to finally destroy itself in evil insanity, violence and perversions . . . and then He gets to reveal other aspects of His character--such as MERCY and GRACE--by stepping in to take the punishment for Himself, in the God/Man Jesus, and save all those who repent of the grand mistake and at last turn to follow and worship Him as Lord--as the ONE AND ONLY LIVING TRUE GOD. . . . It is terrifying, awesome, beautiful and mind blowing--the whole affair . . . and in the end, all revolves again in just revealing the wondrous, glorious, jaw-dropping acceptance and reverence of His "glory"--that HE IS THAT HE IS and He has deigned to make us to be witnesses of the same!
It is a paradox . . . and confounding to the carnal and worldly mind--although comprehensible in a sense to a "childlike" and humble mind--that you really can't "See" until you Believe.
The world-wise would say he wants to "see" first, then he'll "Believe" . . . but this is actually just a dodge by the prideful and ever-resisting. The "wise" of Christ's day saw Him, heard Him, witnessed His miracles . . . and it only hardened their rejection; to the point that they trumped up charges in order to kill the innocent man/God.
The biggest stumbling block to realizing Who Jesus, God is . . . is the fallen, self-seeking, rebellious human mind's tendency to presume how God "ought" to have done things. Why did He allow sin to enter? Why doesn't He stop suffering? Why create beings who are capable of rejecting Him? Why make a world that includes disease, war, rape, theft, adultery and then send the "only Begotten Son" to suffer and die to save it? Couldn't it have been done a "better way"?
If you don't believe in the God Who is love, holy, perfect, all-knowing, merciful . . . then such questions don't seem quite as ridiculously arrogant and presumptuous as they obviously are if there IS such a God. But once He reveals Himself to you--once you have at last come to the end of your limited self and you are truly broken, humbled--an admitted "wretch" in need of a Savior--then it is a small thing to joyfully and confidently accept that, no doubt, the Divine Mind--the Author of All--is doing precisely and perfectly exactly just what is best, for the highest and most good, taking into account all that has been created and how it all relates together . . . through time . . . and as intended . . . continuing throughout all eternity.
I don't doubt that this is an inadequate response, but it is a pleasure to attempt all the same! :) Thanks, and despite my feeble castings, please, please pepper me with more! I have contemplated these matters likewise for a long time and continue to, and can think of little better to be done than talk about the only Subject/Object that could possibly make some sense out of this present disaster:)!