I think it's kind of cool that you offer us a finite choice. I think 1 would be too little and being able to lock down all women (numerically) would be too much.
If you gave us a number that the harem can include like 5 or 10 depending on the total number of women, that would be cool. Maybe that would be better expressed through a percentage, like say 25% of the total number of women can be locked down. But what I mean is you can choose out of EVERY girl, but only lock down say 5 out of 25 or if the percentage is higher 10 out of 20.
Then at the end of the "window shopping" part after we had enough time to see and talk to all of the women, we have a selection screen where we decide how many and which women we want to lock down, because maybe some players will want to just lock down 1 or 2 women rather than the full maximum number that I talked about in the previous paragraph. The women you didn't lock, but are interested in will be shared, the ones that are locked are exclusive to you and the ones not chosen will have relationships with other men only.
Problem is, how you would implement that system when new women are added to the line up since some people might use up all their choices when not all of the women are added yet, maybe the designs can be finalized first or something like that. Your thoughts as the dev ?