I don't feel like I know enough about the property yet to have a meaningful opinion, but I do have one suggestion/thing to think about. Do you plan on building any bogs/raised beds/veggie plots/etc. in the yard as well? Especially since you see some harsh winter weather, a little planning using permaculture principles can save you a lot of money and heartache down the road, and potentially give you much wider options about what you can grow and where.
Small trees, large shrubs, or trellises with something like those wine grapes can provide filtered sun/dappled shade during hot summer months while remaining out of the way during the rest of the year to maximize your winter sun if you measure out your angles right, and serve as windbreaks year-round to protect from storm damage. Properly arranged raised beds can protect against cold drafts that travel low to the ground, or you can get the same function on the cheap by building earth berms from hay bales that have been topped with a mound of compost and then planted with tall grass, wildflowers, or shorter annual crops like fruit-bearing shrubs or Jeruselam artichoke. If you plan right you could both use these techniques to improve conditions for the greenhouse, and use the placement of the greenhouse to enhance your options for the rest of the yard.
By taking into account nearby structures and landscape features such as fences, neighboring buildings, hills/valleys, stands of trees, etc., combined with the orientation of your property in terms of cardinal direction, you can tell where your local weather patterns will come from. Then you use layered perimeters of barriers such as trees, shrubs and berms to divert the wind around sensitive areas. If I recall correctly, a skilled thorough application of permaculture techniques can often allow you to grow plants as many as two USDA zones higher than you would usually be able to - perhaps even more. And when they're well cared for they tend to be very inviting and aesthetically pleasing.
Also, I'm soooo freaking jealous.
~Joe
PS - Also think about a spot for the compost heater. Srsly. It doesn't have to go in this year, and if you set aside a good spot for it I'll help you design and build it as soon as I have the means.