I think you should start in the second update and no later than the third with the first mass-murder.
Jokes aside, you need to make it possible for the player to actually prevent the old man from touching your LIs from the start if at some point there will be romance. The other option is to keep what you have in this first release and just use those characters as sex slaves when you eliminate the old man.
While you might be thinking of the harem as the historic "haram" in which the women were pretty much sex slaves. In the VN and erotic literature community it is generally understood as a romance with multiple women (the women being fully aware of it). While I would say that either approach is valid, it is important that you make it clear to the readers what is your intention.
If you tell your story as a "haram" while it will technically be a harem, it will be understood by most as just NTR. That is because you are just watching your loved ones getting fucked (like in the first release) and by the time you get them to your "haram" the player will just feel like they are tainted flesh to fuck and discard.
As an example. While I dislike NTR, I have played NTR games (they are good smut) because some developers warn you from the beginning and you kind of prepare yourself to not get attached to the characters.
As you already said, you are doing this as a hobby. It is best that you are upfront and honest as to what you want to do with your story. This will lessen the shitposting in your thread, it will make yours and the reader time more enjoyable and you will feel good about your hobby.