while I cannot help with specifics, I can mention (maybe again, perhaps wrote this before when you asked about this trip) that in general, Vermont drivers are really quite good for leaving space for cyclists. I rode from Montreal to Boston a few weeks ago, following mostly the 100 from east of Burlington (so spent most of the time east of that large park area) and the experience vis a vis shoulders and car and truck driver politeness was very positive. Coming into the Killington area along the 100 from the north did involve a pretty good climb, so do make sure you have low gearing for the weight you will be carrying, and that everyone is competent enough for riding slowly slogging up a hill with X amount of traffic going by. The actual climb approaching Killington on the 100 oddly enough had the worst cracks in the road, the type that run parallel to your wheels, so you had to be careful while huffing and puffing up the steep bit.
As always, I highly recommend some type of mirror.
Have a wonderful trip and hope weather is cooperative.