The primary nexus for QEMU developers is the qemu-devel mailing list. (Very high traffic because it's also used for patchmails.) The irc channel is a bit more variable and tends in particular to be quiet outside UK/Europe working hours, just because most QEMU devs happen to be Europe based.

I discourage private emails sent direct to me on QEMU topics (because they should generally be to public lists so other community members can answer them or benefit from the answer), but you can find me on the mailing lists and irc.