Many already asked the same in the past decade and the answer remains: Most events need a certain amount of mixed gender and lacking those might crash the game or simply skip them.
If you, for example, divide classes by gender, game might crash if you are unlucky, and you'll only get about 20% of them trigger.
As much as people attempted to play a harem school game, it's actually a corruption game and the current devs already lack staff to write more events to fill the gaps for every playstyle.
If you do want to try, though, the easiest way is to convert everyone to futa and then all the futa to your preferred gender, and it seems Shilo does plan to make it possible/achievable eventually, judging by the intro goals.