Everyone's favourite time of year to visit Vermont - and the rest of New England - must be October when foliage is in peak. We were probably a bit too early for that (2-4 Oct) or maybe it wasn't the best year for leaf peeping. Still, seeing the leaves changing their colours was beautiful. There was more red than I was used to in Europe. We usually get more yellow/gold/orange over here.
Be prepared that not only the foliage peaks, also the rates for accommodation do. And the traffic does. It wasn't too bad, though, still acceptable.
Book way in advance! Now would not be too soon! You could reserve for a couple of weekends. That way you could keep the weekend with the nice weather and cancel the other one. I used to work in a hotel and things would get so booked up around foliage season that there were NO rooms in the state at all. No kidding, I sent a guy to Montreal for the nearest room! Woodstock is great, by the way, you'll love it.
Fondest memory: A lovely town green. Take some time to stop by Billings Farm Museum and the Rockefeller National Historic site.