I've been to the tailgate several times. Some times there's a ton of vendors, sometimes not as many. There are more early in the day than in the afternoon.
From the buzz on the HV Chickens list it sounds like there will be a lot of vendors this time including people with some other types of livestock - hogs, goats, and such.
They use different sites, but both are on the other side of the Hudson from Millbrook. I think it would be less than an hour for you, maybe about 45 minutes, but I'm guessing. Some parts of Millbrook are down long windy back roads, so you should use Google maps for a really good estimate.