3 is too little, 4 is just right, but I think 5 is the best. Got it from my love for Ouran High School Host Club and La Corda D'oro, I could have more than one love interest if there's much more LI's in the game!
Five is perfect! Anything more makes me feel like their story length would be shortened to compromise or is otherwise overwhelming if you have a completionist mindset. It's honestly one of the reasons why I was put off from 9 R.I.P for so long... (praise me, I've finally started it this spooky season just so I don't come off as a larper for the official cupsleeve event HAHA)
I think 5 is bare minimum! Especially because at least 1 is gonna be childhood friend (I'm very tired about this TBH so it auto cancels out a route for me...) So at least 5 is good for me~ I like variety so long as it does not sacrifice writing~
5 if they all share the same common route. I don't mind more as long as the route divergence occurs early enough that it doesn't feel like each boy's route content is only 30% of play time when you include the common route.
Norn9 did this the best where it's so fresh depending on which protag you play as and you get different perspectives. Hanaichi of course is great too as the route divergence is super early even if the general event flow is pretty similar. Sangoku Rensenki has 3 major "camps" which switches it up enough that it doesn't get tiring.