I will give him this, he should never limp pre with with 53s. If you want to have a bigger open range then mix in hands with more equity like 98s or 97s. More ways to win and just as disguised. Don't call a marginal hand that connects with an ace as an ace is more likely to play the hand. This is a bad open in my opinion - 75s I might give him the benefit of the doubt.
Standard call even out of position. QJs has a lot of ways to have a good to great flop and pay off. Not strong enough to re-raise. Moon should put Kopp on JJ+.
You have second nut and are not the pre flop aggressor. Go for max value. Check hoping Kopp will bet. Kopp could be on like AT diamonds and you are behind. Statistically there is only a 2.3% chance Kopp has diamonds after that board. Kopp with the lone A diamonds is possible. I would still go for max value.
A flush is probably good here. No reason not to bet it. Be cautious if another diamond hits as Moon could have one diamond.
Paired board brings on the possibility of a full house. Kopp is not capped so he could have KK or 99. Check to let the aggressor bet is good. Not getting the raise after Kopp bet 65%. You could be behind here - it is time for pot control. By betting 1/3 your stack you are pot committed. What worse hand is going to call? Kopp is not calling with a single 9 or K. You could get called by a smaller flush. What would Kopp shove with? He would shove with a full house. He could be bluffing and representing a full house. Kopp would not put you on a full house as you should have raised KK or 99 pre. Moon would not likely call pre with K2 or 92. Moon is pot committed so I get the calling the all-in. Moon should not have opened things up with the raise.
The initial bet is too big for exactly what happened. If Moon raises back he is pot committed. I takes away coming back with a bluff. If Kopp bets 40% (1250) and Moon comes back with 3000 it is easier to just get away or have an all-in bluff that puts Moon in a tough spot. The raise from Moon is pretty much never a bluff. That board is scary. He committed 1/3 of his stack. If Moon was bluffing he would shove. Moon thinks he is good and is building the pot. Makes little sense for Kopp to shove. Kopp is not getting called by a worse hand. Assume Kopp is representing a full house. He can represent a full house as KK 99 are in his range. Kopp is almost certain Moon does not have a full house as he should have raised pre with KK or 99. What hands would Moon fold? Right or wrong the paired board did not scare Moon. Moon raised 1/3 his stack - he is pot committed. Moon is not folding here. Should Kopp call or fold. Maybe bottom flush is good and deserves a call. I don't see Moon raising with with a single K or 9. Maybe he is raising with A diamonds and K or 9. A baby flush is a good enough hand to call but consider folding. Moon committed 1/3 of his chips and he is likely to shove the river. Do you really want to put your whole stack at risk with bottom flush here? If the initial bet was smaller and Kopp was only facing 3000 it would be a lot easier to call and hope the river goes check check.
Hand was already over.