Couple things here. First, regarding your choice of skis. I'd think your chances of encountering "firm" conditions are as good, if not substantially better, of encountering perfect powder conditions. Anything "on-trail" will get tracked out in less then an hour, even mid-week. i.e., if it snowed enough overnight to get excited, then the locals will be out, and they'll beat you to it. So I wouldn't worry about picking up something "fatter". If you do happen to be there during a major dump, then you can always get a one-day demo from any of the dozens of ski shops in the area.
Regarding trail difficulties... I skied mid-Atlantic areas for two or three years before making my first trip up to Vermont. My first destination happened to be Stowe. Somebody above mentioned that Stowe's blues are like Pennsylvania blacks; I can assure you that that is true. I spent three days at Stowe with my friends on that trip; we stuck mainly to the blue groomers, and I had a great time. We did occasionally venture off onto some of the single-blacks, and I just remember it being a very humbling experience.
Basically, if you go to the Stowe/Sugarbush area, you'll find plenty that's skiiable in your ability range, and you'll also find plenty of
terrain. Your chances of being there for at least one fresh-snow day are better then your chances in the southern part of the state. If you go to the southern part of the state (Okemo, Mt. Snow, Stratton), you'll find a greater number of trails that you'll find enjoyable at your ability level.