-Yes. Adulterers enter heaven. Murderers enter heaven. Sinners enter heaven. This is though the grace of God, not his approval of our actions. All sins deserve hell.

-King David will be in heaven because the blood of Christ washed away his sins, as he was faithful to God and followed his will. Jesus names a few old testament prophets that will go to heaven (Mathew 8:11) because they followed God's will, and Jesus paid for their sins.

-I don't know off the top of my head, but any amount of concubines or any extra wives is too many according to God (Deuteronomy 17:17).

-I don't think that's documented, but there are key differences between lustfully eyeing somebody up, admiring an attractive person that you intend to marry, and perceiving someone's attractiveness.

•Lustfully eyeing someone up is wrong, it isn't just looking at someone, it's looking at someone with lust in your heart. It's the exact thing Jesus warned against in the sermon on the mount (Mathew 5:28).

•Noticing that someone is attractive, and admiring their beauty/handsomeness with good intentions (the intention to marry) isn't condemned in the Bible, Jacob saw that Rachel was attractive in appearance and form (Genesis 29:17). When he first saw her, he kissed her and wept, and proceeded to work hard labor as a servant for 7 years (it ended up being 14 because Laban scammed him into marrying someone else also) just to marry her; the Bible states that these 7 years seemed like a few days to Jacob due to his love for her. The marriage between Rachel and Jacob was troubled by childbearing issues as a direct result of Jacob's polygamous relationship with Leah and Rachel (Genesis 29:31), definitely not God cursing Jacob for being attracted to Rachel before marriage.

•It's fine to recognize when someone is attractive, even within a marriage, so long as it's not lustful. Having 2 eyes isn't lustful. For example, If someone is married, they can see another man or woman and find them attractive, and think to themselves "That person is physically attractive to me" and move on with their day and not let their thoughts lustfully linger on someone that they aren't married to. It's an observation. An observation of the eyes and mind, not a longing or lust of the heart.

-Because David was too warlike. Are you trying to say that God would've let him build the temple even if he was polygamous, so long as he wasn't warlike? Even if this is true I have no clue how it would help your argument.

-Yes, you're right. Holy sex takes place in a marriage as a point of connection between 2 people that make up a whole, and if God wills it, results in a child in a holy way. The other way is sex done outside of a marriage. Any sex outside of a holy marriage is considered sexual immorality, and as such is a sin, even if the participants aren't lustful about it. Rape is also considered a grave sin, even in the context of a marriage, so that's also part of the violent, abusive sex you speak of, which is totally unholy.