Is October or November the better month to visit Sonoma - weather-wise and crowd-wise??

Dear wanderer,
Weatherwise, October is usually the better month. I say usually because right this moment in the Bay Area we are having markedly cooler temperatures than normal. Where o where did our Indian Summer go?
October does tend to be more crowded, both in terms of tourists and also with vehicle traffic from the harvest labor.
November - well, it is less crowded, the weather can either be sunny afternoons with chilly evenings or it can be the beginning of the winter rains. It does get dark awfully early, so time your driving accordingly.
If it were me I'd choose sometime in November before Thanksgiving.

Is all of October usually good weather, or just the first half?

Usually, yes. But you can't depend on the "usual"!
I've experienced Octobers in the Bay Area where the hot weather extended into the first days of November. Also years when the first howling,drenching rainstorm of the season arrived before Halloween.
In what I think of as a "classic" year here, the first two weeks of October are in the 80's or so, gradually cooling off to the 60's by the last week.

When is crush?

We just returned (well 3 weeks ago) and they were starting to pick the grapes, a bit later than usual. I agree with the other posts, October will be better than November. So what are you waiting for?

I'd say Ocotber.