Sparkly,
Re: boys and girls talking.
It depends on what you meant by “talking.” If you mean “hello, goodbye” and that’s it, there is nothing wrong. Similarly, business talk if they work in the same company, or are trying to sell/buy something in a store is not a problem. Flirtatious/Fun talk is absolutely forbidden outside of the context of dating (although I am not certain on the basis and parameters of the dating heter).
??????? ????? ??????????? ???????????? ????? ?????. ???????? ??????? ????????? ??? ??????????? ????????? ?????????? ??????? ????????????. ???????? ???????? ???????, ??????? ??????? ???????????? ??? ????????? ???????????. Shulchan Aruch Even Ha’Ezer 21:1
According to most, this issur is Rabbinic as a fence to prevent issurei d’oraisah.