[naked_lego]

Reading a kinky fanfic of the younger students would feel kinda weird, personally. But I would still give it a try. I'd suggest focusing around the older years.

I like the idea of having the main characters in it but also I think you could make a really interesting story with new characters. Some that haven't really matured.

Overusing magic could make it unbelievable. Like There should be limitations so that not everyone can just go around casting a spell that enchants someone or removes there clothes.

I find it that first person is easier to write but third allows you to give more thoughts from all the characters. First kind of makes it mysterious like you don't know what the other characters are going to do.
Maybe try writing the first few paragraphs in both perspectives and see what you think fits best.

You should definitely focus on both boys and girls.