Having a friendly relation with the carnations is probably better than sexual relation. You can learn more about them that way.
That depends very much on the character in question! Felicia for instance is easier to get close to if you are both mentally and sexually compatible, you even have a talk about that in her Porsche.
If you bang Rosi first opportunity on the other hand that will make reaching her more problematic. Veronica is also different as a lesbian-leaning bisexual and closet sex fiend (even a well-meaning Edwin can raise her lust stat rather more easily than with others). You have to first click mentally before any deeper sexual relations are possible with our gym owner.
Same with the other love/sex options.Hana you have to convince you are halfway ok as a person first, before real fun stuff can happen. Mina too, but to a lesser degree due to her sex bucket list.
Kath on the other hand uses sex as a tool, you get close to her by showing you are as sadistic and peverted as she is. Sophia is very much about mental challenges and her eccentric mindset to click with her.
I to am Gen X, and watched Jem when it was out. No excuses!!!
Different regions of the world playing a role her. As I mentioned in a deleted post, here we grew up with own productions, American, British, French, Italian ones and esp. "early" Anime.