You can contact the various North Country Trail Association chapters through the NCTA web site. They will be glad to give you pointers regarding how much road walking there is. From the NY border thru Allegheny National Forest down into Clarion County the trail is off road and on tread.
I notice, Lemens, that you live near a new section of the NCTA that will be dedicated on National Trails Day, Saturday, June 7. There's a celebration from 10am to 2 pm from Great Trail Tree Farm, 5900 Pancake-Clarkson Road near Fredericktown OH. For details contact
[email protected] or 330-227-2432. I wish I could be there, but I'll be out of town.
Also, you can find a journal covering portions of the trail south of Allegheny National Forest here: http://www.trailjournals.com/entry.cfm?id=465097 The journalist, Lakeland Nidhatak, used the NCT as part of the route he was walking from NYC to the Pacific. (He wound up ending his hike in Beaver Creek SP). His journal will give you an idea of the NCT south of ANF.