I know how "vague" the "harem" part is, but i tried to min-max the routes and if I did things right, FOR NOW the max i could get was 4 at the same playthrough, the conflicting routes are:
Ashley and Jenny (Dorm or Date)
Aurora and Elizabeth (Study)
Sung Ji and Vicky (meet before date/cinema)
Rebecca, Jade and Valery (Pool or Gym)
So the most optimal routes are (least conflicting, personalities and point-wise):
1. Jenny + Aurora + Sung Ji + Rebecca
(Well Jenny is covergirl which means she's probably will have more screen time, also Ashley, even on this route, still pretty determined to be with MC [as she tells Jenny at the ending of ch.4] and Jenny is only "interested" in MC on Ash route / Idk, but Sung ji on Jenny route is safer since on Ash route you basically have to "lie" saying you aren’t interested on Ash / Aurora or Elizabeth is kind of irrelevant, go with your personal taste / Rebecca is the safest route since her scenes don't conflict with almost anyone besides Jade and Val and she explicit tells that she's cool with sharing, also, she is cute as fuck... btw Val route could conflict with Jenny too, so that don't work well here)
Then:
2. Ashley + Elizabeth + Vicky + Val or Jade (I recommend Val since she is more relevant plot wise, for now at least, but on the other hand, Jade has more sex scenes
...)
For getting most of the content with the minimum playthroughs.
EDIT: Couldn't managed to get Vicky+Ashley, although i remember getting it to work on BETA... maybe i'm delusional, made a wrong choice this time or new variables are set, this time in Vicky "confession" scene the MC straight up tell he has feelings for Ashley... Weird
...
