Now you should tell us -- IN THE LIGHT OF GOSPEL TRUTH -- whether any of these statements are true:
Of course they're true, once you understand the perspective from which they are written. Solomon was a king who "had it all." He had wisdom from God, wealth beyond measure, 700 wives and concubines, and even though he did many ungodly things in his life, he came to realize that without God and the promise of everlasting life, everything he had basically counted for nothing.
1: 2 Vanity of vanities, saith the Preacher, vanity of vanities; all is vanity.
See above.
1: 9 The thing that hath been, it is that which shall be; and that which is done is that which shall be done: and there is no new thing under the sun.
That's basically true. There is nothing new. Things get recycled and happen at different times and in different ways, but nothing is really new.
2:20 Therefore I went about to cause my heart to despair of all the labour which I took under the sun.
See above. All of Solomon's wealth, wisdom, and accomplishments, without God, are basically worthless.
3:18 I said in mine heart concerning the estate of the sons of men, that God might manifest them, and that they might see that they themselves are beasts.
3:20 All go unto one place; all are of the dust, and all turn to dust again.
6: 6 Yea, though he live a thousand years twice told, yet hath he seen no good: do not all go to one place?
6:12 For who knoweth what is good for man in this life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?
Because you believe that the human soul is immortal, you cannot accept that those statements are true. No part of a human being is immortal. There is no "immortal soul." What happens to both men and animals at death is the same. They die, and cease to exist. People who die will not exist again until they are resurrected by God.
7:3 Sorrow is better than laughter: for by the sadness of the countenance the heart is made better.
That's also true. We generally learn more, our heart is made better, from negative experiences in life than from being "happy."
9:5 For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten
That is absolutely true. The New Testament did not change the definition or understanding of death. Dead people know nothing, their emotions have perished (Ecc 9:6), there is "no work, nor device, nor knowledge, nor wisdom, in the grave" (Ecc 9:10). The dead cannot praise the Lord (Ps 6:5; 49:12; 115:17; and many more). Our hope is in resurrection, not in dying.
I know how you respond to people who have beliefs that you personally do not hold... You will accuse me of being in a cult. Go for it.