Just some thoughts thus far:
First, big fan. Loved this game since its inception, or more pointedly since MC fingered Mimi during massage (damn erotic!).
1. Martin. Bet Walkius didn't expect the anti-NTR brigade to come bearing pitchforks and torches, huh? Screw them. I think Martin should be expanded. He should have a shot at nailing all the ladies of the house (hell, go nuts, why not Emily or Ako at the sleepover?). It should also be easy to disrupt him if that is your desire. Befriending him should have at least 2 tangible benefits: 3-somes with Mimi and later with his girlfriend. Letting him continue to bang Maria should also have him tutor MC into doing the same. That sounds pretty hot to me, your mileage may vary.
2. The teacher. Would at least like to delve a little into her.
3. Ako and Alice. I love that Ako gets a turn with Alice (who conceivably could be getting nailed by Martin, MC and Ako!), and that Ako is also doable for the MC. There should be some serious seduction in other settings, as Alice could chalk up the sleepover to a one time thing, alcohol, etc. Have Ako seduce her in other settings, with the help of the MC.
4. Stay the course. Whatever is decided, this game rocks. Loving the updates and all the girls in it. Don't forget the bartender!