If you put the first coat of Proofide on your Brooks, you'll be OK.

Regarding the helmet, my opinion is that it is dumb to commute without a helmet. (rain or no rain) You should rectify that ASAP.

Regarding the jacket, does it breathe enough not to make you hotter? I've found that with rain jackets, I still end up wet, but from sweat instead of the weather. Plus I stink more. I'd rather be wet from rain and not stink too.