It's up to you how u wanna make your game ,but mixing Ntr and harem maybe is not the best way ,those tags rarely go together and, succeed you need to choose what kind of audience you want and go that way .
And if you gonna make sandbox style game it has to be good , with clear instructions what to do and where to go so people won't waste time on searching themselves and plus if there is gonna be some kind of grind like working making money or anything like that the players has to have a pay off for the things he will be doing,not just to waste his time on it (i don't like sandbox i think is a waste )
All in all wish you good luck , hopefully you'll succeed but I'll move on from this game is not for me i am a harem player,but no sandbox and no tags mixing like that,take care.