1. None that I know of. Suggestibility is now the means to invoke trances during orgasm. If you don't mind save-scumming, you can make do with the first Suggestibility serum trait the whole game. I don't recommend it though lol
2-3. Vren introduced sluttiness caps to various means of increasing sluttiness, just like flirting would only work up to a point. As a girl's sluttiness increases, she'll need to cum from more and more exciting sex acts to raise her sluttiness. I feel like the values for all of the caps probably need to be tuned, but it's good to see Vren is trying to address the "bored with this" problem. One thing that doesn't appear to lose its effectiveness to raise a girl's sluttiness is to cum where she likes/loves it. If the girl doesn't have a cum preference, train her to have one of your choosing, or retrain her if she does have one you don't like
2-3a. There's an increased temporary sluttiness buff from arousal now. Getting her turned on really helps a lot. The serum that raises arousal cap can get a girl to do a lot more than she'd be willing to otherwise, but IMO the increased effort to make her cum multiple times isn't worth it. I still prefer the serum that lowers arousal cap for the ahegao effect, especially since arousal lowers less with each time she cums now
4. Sexual opinions re: positions raise/lower her arousal gain from sex in that position. Sexual opinions re: where you cum raise/lower her sluttiness when you cum there. Bareback sex opinion raises/lowers her willingness to sex without a condom and raises/lowers her arousal during sex without a condom. Sexual opinions re: public sex raise/lower a girl's excitement while playing for an audience, including if she's just watching now. Sexual opinions re: clothing/exposure raise/lower sluttiness when you undress them or if they're exposed in public (protip: train your girls to love "not wearing anything" to negate the arousal loss while stripping and "showing her tits" and "showing her ass" to raise arousal when stripping her tits/ass bare). Did I miss any?
5. I got Jennifer all the way to over 9000! er, sorry, over 100 sluttiness with creampies since she loves them. Cum preference really makes a difference now. I'd recommend you train your girls with the cum preference of your choice, followed by the exposure ones I mentioned above and maybe public sex if you like playing with your employees together (since the new onlooker bonus improves a girlfriend's willingness to overlook you cheating), followed by one or more of your favorite positions. Don't forget to order your girls to strip often and check Insta/DikDok/OnlyFans to farm clarity, and rotate which slut you use to keep novelty high.
Oh, novelty is new too. It lowers for a girl every time you cum with her and raises when you break a new taboo with her, and recovers a little on its own each day. Lowered novelty reduces the amount of clarity you get while cumming. You'll see a message when that happens