but I think it's hard to pull off well because it's too easy for a blank slate protagonist to come off as boring or just plain empty. A protagonist with a more defined voice and history is usually more interesting off the bat
Like with most things, it's a give and take. A pure blank slate can be boring, but it can also give the player the freedom to decide for themselves who they want the main character to be. Meanwhile a "blank slate" that the player can shape via choices can make for a far more interesting and immersive story, but it also requires more work on the part of the dev to juggle conflicting dialogue/plot branching (ie, if you give the player the choice to decide if a specific LI is their childhood friend or childhood rival, you now have to plot out two different paths for how that character interacts with the MC).
The problem with fully fleshed out and defined MCs is the same sort of give/take - the advantage is that the dev/writer can establish deeper aspects to their history and personality that can play out as a more complex story, but the disadvantage is that they may wind up writing an MC that lots of players utterly loathe (see also the perennial complaint of many players about doormat MCs or total asshole MCs in games). In the same way, you risk having the MC feel specific ways about supporting characters that conflict with how the players do (ie, having your MC pine after an ex while most of the player base hates the ex and just wishes the MC would just get over it, or having the MC chase after a LI that most players would rather just avoid entirely).
There's also the issue of whether or not you're dealing with players who want to put themselves in the shoes of the main character versus players who just want to watch someone else's story play out. The former group will tend to like flexibility and the option to make choices and influence
their version of the main character's history, backstory, personality, and relationships... while the second group will generally get more out of a deeper, more complex story they have less power over.
Mc will meet 5 women. This was my assumption at the beginning of writing the script. But this number may change.
5 is a pretty good number for LIs. Fewer and it can feel like the player has less control/options or not enough variety, but too many more than five starts to become unwieldy to write and harder to put focus on any one individual LI (so they all start feeling underdeveloped and less interesting).
There will almost certainly be a temptation to add more as you go, either because you get new ideas, or because people promise to throw money at you on Patreon if you add [insert character stereotype here]. You'll probably be better off if you resist that urge and generally just stick to the characters you originally planned for and are putting most of your focus on. Don't let the story grow out of your control as you keep adding more and more peripheral LIs to avoid furthering the main story (way too many devs do this).
As for the harem tag .
I don't think it will work out. The game is moving in the direction of facing consequences for the choices you make. I can try to implement this in the game, but I am afraid that the MC might end up cut into pieces in a garbage bag at the bottom of a lake.
Having games where your choices matter and you can really only pursue one LI are fine. Games where you're essentially punished for trying to pursue every love interest/try for the harem route are fine. Having to choose between potential options can make for deeper stories, and the conflict between choices can make for emotional storytelling. This can be great.
But the rule of thumb you might want to keep in mind is a) you should make it very obvious early on that players are going to be expected to pick one LI and will probably get punished for being too greedy, and b) you should at least give players
some leeway early to play the field a bit before drastic consequences come into play.
Become a Rock Star actually handles this pretty well - for most LIs, you can kind of flirt and even get a bit intimate with multiple girls early on, and it's really only at the point where you explicitly commit to a serious relationship that you get punished if you try and string along more than one girl. So the player has time to get to know the different LIs and decide which one they prefer before committing to one (which also helps encourage the desire to potentially play the other routes out, because the alternatives are now interesting and appealing in their own right, and not just generic ciphers you mostly ignored in favor of hyper-focusing on a single LI).
I'd recommend something similar, if possible - allow the players to have meaningful interactions with all of your LIs early on, potentially with a couple casual sex scenes each, before you reach the point where you have to pick which one to get serious about.
I'd also lightly discourage from making the consequences for choosing one girl over another
too disastrous - if choosing Girl A causes Girl B to die in a fire while Girl C kills herself, even people who absolutely love Girl A may never want to choose her (and will kind of hate the game for being so cruel). Sure, there can be terrible consequences for characters (especially if the player is making
bad choices), but players should never feel entirely helpless or powerless to keep most characters relatively safe and happy.