Ah!Ah! I know that, I mean one of the game in my sig is pretty informative about the fact that I'm worse than a kid in a candy store, if offered a choice of course I want all the candies!!!
But on a more serious note, the big flaw I've seen in harem games is the time frame for every girls; the more there are the less time there is for everyone of them to be, not only romanced, but developed in a good way that's not "Hey we have an MC with a magic dick that make them fall for him".
I mean girls that have a distinct and defined personality that can be pursued romantically, plus convinced to share the MC after being in a relationship, this already a lot of work.
The games that solved this issue keeping a good balance are relatively few like Sisterly Lust, OIAL, Mythos, Long Road home, Sorcerer ( but this was already at the limits) and in all of them the solution was to keep the number of LI's limited ( and or inside a familiar circle or with a good reason for them to be kept together).
I mean it's good to have some side girls to have a distraction, but if you really want a good harem path I think limiting the main LI's is essential, at least when starting developing a game, you already wisely said.
Another thing I would take into consideration is to create a main LI, a girl that could work both in a solo but also in harem path, I think it's essential to have someone to be equal to the MC, imho is way more interesting.
But I think you already thought about all that, so sorry for the wall of text, can't really wait to see the final result so good work!