There are posts every year in this forum about trying to predict when the foliage will happen in certain areas. It's really a crapshoot, but here are some threads that I hope are useful:
http://www.flyertalk.com/forum/new-e...lime-rock.html
(and note post #8 by
tkey75 stating how the foliage in BTV was past peak already, dated September 28, 2010)
http://www.flyertalk.com/forum/new-e...eekend-ne.html
(has a great link to a foliage predictor in post #3, and according to the predictor, most of New England will be in 'peak' territory during your visit).
With regard to your other questions... Personally I love the Kanc (as the locals call it) and would normally suggest that many times over the ferry. Just keep in mind that foliage traffic, combined with traffic for the Fryeburg Fair in Fryeburg, Maine will make the Conway side of the Kanc VERY VERY crowded. So be sure to plan accordingly if you go that route.
I don't have much expertise in any of the other points you raised, so hopefully others can chime in.