Let's see...
1) I'm pretty sure you're right about this one. As far as I know, only women are ever called Brightness.
2) Somebody asked this on Tor's Q&A session. He RAFO'd it. Whatever the distinction between the epochs is, it must be important to the story.
3&5) If there are different names, they don't appear in the book. Somebody should try asking Brandon (though that sounds like something he'd RAFO.)
4) Presumably, the only Gods hanging around Roshar are The Almighty(Honor), Cultivation, and Odium. The only one who seems to be commonly known is The Almighty. The Heralds apparently served The Almighty before breaking the Oathpact and going their separate ways. Whatever powers they had came from The Almighty. So, no, they are not gods themselves, but they may have enough power to convince others that they are.