I’ve enjoyed lots of winter backpacking in Pennsylvania when the snow is not deep enough to demand snowshoes, so *as a frame of reference*, here’s my two cents:
1. What sort of boots are recommended?
Most winter trips I find myself post-holing through similar amounts of snow, often more, and lightweight hybrid boots like the asolo fusions have served me well enough. I've found them to be a good balance between the stiffness needed for kicking steps into hard snow, and the flexiblity we all like about trail shoes. Synthetic/leather hybrids will lose a lot of structure (ie. ankle support) after days of snow-trudging, but with a light pack, I've found that to be a non-issue. all-leather models will fare much better on this score, preventing the boot-cicle effect somewhat. Either way, stow them inside your sleeping bag at night and you should be okay.
2. Is it necessary to use a dome tent or can I get by with a tarptent?
Tarptents can be great for moderate winter conditions -- I have a solo caternary-cut Oware tarp, with homemade beaks that make it near fully-enclosed (similar to the forthcoming GoLite Hut 1, see BPL first looks) which is my standard for winter trips when there's not much danger of heavy snowloads (collapse!).
A few tips are in order here. You should seriously consider a very breathable bivy sack (Pertex Quantum is my choice) for any non-breathable winter shelter. I’d hesitate to spend more than one night in the backcountry without mine, if that, and mostly I use a synthetic bag in winter. Also, a snowclaw mini-shovel or something similar is essential, even if only for digging a recessed platform into the snow. In cases of unexpectedly heavy snowstorms, use it to relieve your site of excess snow a few times throughout the night, or to build small windbreaks if things get especially nasty. Just gain experience gradually if your unfamiliar with tarping in winter. (I’m guessing you’ve already noted the technique article on tarping in inclement conditions.) That said, I’ve never been for want of a better shelter in winter conditions with moderate snowfall. And unlike a tent, you can dive under it with boots and snow-soaked gear, cook safely and warmly (esp. with anything short of a white gas stove), quickly pitch it during inclement lunch breaks and emergencies, and in general enjoy a lot of versatility / worry-free-ness that a tent just can’t match.
4. Will I be ok with the following layers: Thin wool base layer and R2 vest (or V-trail top without wool base layer), lightweight insulating layer (MEC Northernlight Pullover), and a soft-shell jacket?
This is the part that really perked my ears up! Clothing is often the most debatable issue, and in winter esp those stakes are high. I’d scrutinize this clothing system very carefully. For instance, I currently use a woolie base layer and montane litespeed for winter, but I am definitely keen on the V-Trail possibility for better breathability. Synthetic insulation is also a smart choice. However, the stretch-woven softshell jacket might be your biggest liability (based on my experience w/ jackets made with schoeller dynamic and cloudveil inertia). Others will disagree, but I'd agrue that the controling difference here is location. Even in PA -- and even in Jan and Feb -- I’ve frequently seen unexpected warm spells that bring freezing rain and sleet most of the day, when snow was forecasted, before temps plummet again at night (or at least freezing rain during the warmer parts of the day, when wet snow morphs into something even wetter). Stretch-woven softshells are problematic by the third to fifth day of a trip, unless you’re maintaining relentlessly high aerobic levels by day, and making no mistakes at night in regards to drying that wet stuff out. Note once your average stretchwoven is soaked, it can be very slow to dry, and will certainly lose much of its breathability.
On trips when I’m certain that temps will be low enough to prevent freezing rain, I have swapped the hardshell for a schoeller jacket. The breathability and comfort of these fabrics are impressive, but I think they earn their pricetags best in drier winter climes than here. For anyplace as far south as Shenandoah, I’d suggest the most breathable WP/B hardshell you can get. I just snagged an ID eVent jacket which so far has performed well in cold and wet conditions, though I’ve had little chance to test it in temps below the high twenties. Due to the higher risk of trapped condensation in cold temps, I wouldn’t layer it over a down pullover, but over a Polartec or R2 Vest while on the move, or in addition to a synthetic pullover at lower aerobic levels or colder temps, I’d trust it over a softshell *in this context* Incidentally, while the lightest stretch-softshell jackets weigh just under a pound, the combination of an eVent jacket and a cocoon pullover would weigh only a few ounces more, be as cheap or cheaper than the MEC+softshell combo, and would be more versatile for cold and wet conditions, IMO. The synthetic pullover can be used similarly to a softshell, while the WP/B provides the protection for wetter conditions. The compromise is a certain amount of breathability, on both counts, but throwing an R2 in the mix gives one more options for breathability. Don't get me wrong, I’ve used the general softshell approach with great success in fringe 3-season conditions, often wearing only a base layer and windshirt in conditions where others don the gore-tex. But I’d encourage you to experiment, and find your own limits before making that decision. a long dayhike in moderately chilly drizzle/rain with a v-trail, or base layer and windshirt, could help place your own requirements in relation to others.