Hope you don't mind me just diving straight in to tackle your questions directly.
Why didn't God just kill Satan instead of letting him wreak all of this havoc?
We need to keep in mind that the reason why sin and death exists in the world isn't because of the devil, not really, but because
we screwed up. St. Paul writes that sin and death have reigned since Adam, because of Adam's disobedience, death has come to all men. It's not the devil who screwed up our world, we did that. Now the devil tempted Eve, sure, and the devil tempts us--again, sure enough. But devil or no devil, the problem exists, and that problem has to be solved somehow.
So, perhaps a better question is, why didn't God just destroy Adam and Eve and start over with a fresh, righteous family to repopulate the world?
Well, if we pay attention, that's basically the story of Noah and the flood. And here's the thing, in the story God destroys all the wicked people and keeps only "Righteous Noah", his wife and kids and their wives; and gives them the same commandment He originally gave to mankind in the first place, "Be fruitful and multiply". This is, more or less, the story of God starting over, of God erasing the whole thing and beginning again.
And here's probably the whole point of the story: It doesn't apparently work. Immediately after the waters recede, and dry land shows up, Noah rushes out and builds an altar to praise and give thanks to God (well, that's a pretty pious thing to do, good on him)--and almost immediately after we see Noah, drunk and naked in his tent, and when Ham enters and sees his father in such a state, Noah curses Ham. Apparently "Righteous" Noah wasn't so righteous, and apparently just killing off all the wicked people didn't actually fix anything. In fact it's not all that long until people get it in their head to build a tower to reach heaven because they're arrogant and prideful.
From a Christian POV, everything after seems to be the story of God fixing the world. And it's all leading up to a crucial moment, and that moment is when Jesus Christ is nailed to the cross.
We see, then, how God is fixing the world, how God addresses the problem of evil. It's the Crucified Jesus. God made flesh, condescending into our broken messed up world, to share in our broken messed up humanity, and to die a broken messed up death because in swallowing up all our brokenness and messiness in Himself, He takes it, kills it in His own body, and then--and this is the good news--He rises from the dead having completely overcome up. And now, invites us all to partake in Him, in His victory over death (our death) over sin (our sin) over hell, and the devil, and all the wretchedness we see in this world; to hope in Him, to trust in Him, so that we will stand with Him and in Him on the Last Day when God, in Judgment, consumes this all up in order to finally and fully free creation from these things.
Why doesn't He do this sooner? Well, if I had to hazard a guess, He wants to save you too.
And why did God even create us in the first place if He supposedly lacks nothing?
Short answer: Who can say?
Long answer: Well we could write entire books on the subject and delve into a lot of really fascinating, but really complex philosophical and theological discussion. For example, one could speak of the fact that the Logos, who became flesh in Mary's womb as Jesus, who is Himself God from the Father, and through whom all things were made is Himself already tied into the created world because (after all) in the Incarnation He became human, part of creation. And perhaps in some sense it may not even make sense to even speak about God apart from the fact that He is the Creator of the universe. Many people a million times smarter than I have spilled a lot of ink saying things that I don't even know that I fully understand.
So, I tend to stick to the short answer: I don't know.
Finally, why is God going to make us all go through what the book of Revelation describes?
This question is complicated by the fact that not everyone (that is, I mean Christians) reads the Revelation the same way. And what I mean by that is that not everyone reads it as predicting or speaking about a future period (a view known as Futurism). Historicists believe the Revelation speaks of events that span across history, from John's time when he wrote it, until the Last Day when Christ returns (thus, in some sense, we're living in the time of the Revelation now, and have been for the last almost two thousand years). Preterists understand the Revelation to specifically be about John's own time, and shortly thereafter. It's not speaking about things happening hundreds or thousands of years into the future, but what's going on then and there while he was imprisoned on Patmos. Idealists would say that trying to locate the events of the Revelation at any specific time may miss the point entirely, and that the thrust of the text is what it's saying about God's victory over and against the world through Jesus Christ, and thus whether there is tribulation under Roman tyranny (as John and the seven churches of Asia were) or Soviet tyranny, or some future tyranny--we can always look and hope in Jesus Christ who has overcome the world, who will come again and set all things right.
Me personally? I'm somewhere between being a [Partial-]Preterist and an Idealist. I don't believe the Revelation addresses a future period of time under the rule of global tyrant; but addresses the tyranny of Rome in persecuting the Church, but more importantly points to Christ as Victor over all tyrannical and worldly power so that regardless of whatever tribulations we encounter we can always trust in Jesus, the Lamb slain before the foundation of the world, worthy to open the seals, who was dead but is now alive and has the keys of death and hades--who is coming again and very soon, in glory, to judge the living and the dead, and set all things right.
Now after having said all that: there's nothing wrong with having questions such as these. Having such questions is healthy, challenging ourselves is how we grow.
-CryptoLutheran
