I've allways worked it cold, with frequest anealing. Doesn't seem to flare until it gets to melting temp in my experience.
While technically brass is a copper + zinc alloy, and bronze is copper + tin, there are a lot of commercail bronzes that really either brass, or have other alloy elements. Some forge great, some don't. The copper/tin stuff and copper with just a little zinc seem to forge ok.
I've been told that some copper alloys (brass, bronze, gunmetal, etc...) have been alloyed with some nasty stuff health wise, even worse than zinc. You might want to confirm the alloy before you heat it.
J