I'm a fan of group sex/orgies, and it's not as common in adult VNs as you'd think (probably because it's hard to render), so I hope that doesn't change. Good luck on the game. Hope it sticks around.
As a guy developing an amateur game that focuses heavily on group sex/orgies, I can tell you that the main difficulty isn't rendering: it takes more time, sure, but not so much to become prohibitive (
posing, on the other hand...)
The main problem is all the players that hate it with a passion. ("Only dick must be the MC's one" + "Lesbians? I'm out.")
To nobody in particular:
As per the president/prime minister thing: wasn't Japan one of those countries, like my own, that have a President of the Council that English speakers insist to call Prime Minister?
EDIT: I checked on wikipedia, so somebody with some actual knowledge of Japanese politics should confirm this, but it seems I remembered correctly and the Japanese Prime Minister is actually a President of the Cabinet.
To avoid misunderstandings, I'd still suggest to call him "Prime Minister" but using "President" as an onorific as in "And now we'll follow the speech of our Prime Minister, President Tachi."
His "Vice President" could be the Chief Cabinet Secretary or a minister of key importance, like Internal Affairs (or maybe in this 'verse there's a Ministry of Demographics).