GloriousRightFoot
Going to toss my vote towards 4-6 official wives + the occasional kunoichi or other future loyal retainers that make sense. Political marriages are expected, after all. Just because he's lewding several people doesn't mean it has to be the primary focus every time it happens, though the more notable scenes are nice to read about.
Three is enough, IMO -- as long as they end up learning to get along. I have never liked the stories that use the women as a foil for showing the corruption in the royal family or the politics of the nation. We don't need them playing cutthroat with each other -- Nobu is going to have enough drama as it is, and that weakness would be too easily exploited. I suggest Nohime and Yui come together against some "interloper" (like Suzune?) and then you give us a surprise third. Not that I am the author... so take it all with a grain of salt. :)