Yay!

Is there any pattern to this collection of characters? Yuuka and Flandre are said to be crazy and strong, Flandre and Cirno come from the same game, Keine and Cirno aren't that dangerous to humans, Flandre and Keine are linked to the night (Keine's were form). I don't see the overall connection here.

Yuuka loves kids&chibis?

That's pretty much what fanon says. She'll FUBAR you six ways from Sunday unless you're adorable.