In order to address your approach, I figured to trim your post and answer some of your points.
I was taught the Gap theory this way. The Gap is between Genesis 1:1 AND1:2. A period of unknown time between the beginning and the re-creation as Larkin and others believe. Dr. DeHaan wrought several books on the subject.... Then God created man xxxxxxx number of time later.
Problems abound with this theory.
First sin is said to have entered the world when man sinned not satan by scripture.
Why?
Seems that when Satan was found with iniquity that was when both heaven and earth became polluted by his presence.
If you desire to use Romans 5:12 as a support for man's fall bringing sin, then you would be supporting the thinking that Christ's death took "away all sin." (1 John 2:2). Such thinking would do away with hell, heaven and even the fallen angels would be saved from their appointed fate in the Lake of Fire.
But, because that is a false belief, the "world" then of Romans 5 must also fall under the same limits.
Second the number 7 is specific in it's reference to spiritual things, it represents spiritual completion.
So? We all have some understanding of numerology. Some do more with it than others. I am not certain that going down that road would be supportive to your statements.
Next Genesis 1:1 says in the Beginning, what beginning?
Pretty self evident what the beginning is.
Is there a start before God?
What is "time" to God?
Where is the start of God?
Man doesn't comprehend the eternal aspect of always was, is and will be. So, what makes mere man think that God didn't have other creative work before this earth?
Is it because we would box God into what we can comprehend?
Those are all rhetorical questions, no need to answer. The answer shows the foolishness of how some approach the subject from a myopic perspective. At least you have a more understanding of the topic.
Did God create the earth without the moon and stars?
He certainly could have. It wouldn't have been much of a problem for God.
If there is a gap no life forms would have existed the earth could not have sustained life because the Sun, Moon and stars were not created until the
4th day according to scripture verses 17 and 18, God set them in the firmament in heaven to give light upon the earth and to rule over the day and over the night.
And this is supported by what reasoning?
God having placed all the vegetation upon the earth one day, couldn't have sustained the life for the next day. The sun, moon and stars, have no life in them self. They do not rule over the day and night to "sustain life." The scriptures teach that Christ is the life giver and sustains all things. (Col 1:17)
If the Gap existed it served no purpose in Glorifying God and His creation.
I taught the Gap theory for many years until I studied Scientific Creationism and The Beginnings under attack. both excellent books on the subject.
God created the Earth to sustain light for man and according to scripture He did it in 6 literal 24 hour days and rested the 7th.
I agree.
There is no purpose of the preexistence in Glorifying God and His creation for THIS era of existence.
BUT that doesn't mean that it didn't exist, nor that there is evidence of the existence.
For one to assume that nothing existed before this present era involving humankind made in His image is a denial of one of the fundamental characteristics of God being the Creator.
Just because the Revelations closes the door on the present time view of eternity has no bearing upon God's creative work being manifested in whatever He chooses after revelations.
There really is no significant evidence that I have seen in your post that would not allow for the gap and a literal 6 day creation.