The size of Collinwood is a mystery... I wonder if Maine has any mansions going back that far. Come to think of it, that's the biggest damn house i've ever seen in my life, and in any era, only a handful of people live there, and they all hang out in one small room right next to the front door. They keep both wings closed and just use the middle bit.
Don't know about Maine, but the mansions from that period in the NY area are much more Federal Style (plain front kind of boxy -- all the ornate stuff is INSIDE).
Your post got me thinking about a few discussion threads on just this topic on one of my yahoo groups (which alas, went dormant due to some fannish stupidity a few years ago, and I am going to make another crack at waking it up.) ds history vs. melodrama is the name of the group, and we had a really good group for a while discussing the real life history vs what DS shows. (anyone interested in the group please pm me.)
In any case, from what i remember from the posts on this, the size of the house can be explained by the Collins trying to ape the "stately homes" of England of the 16 & 1700s -- I remember Blenheim Palace used as an example. Folks in those days, especialy the rich ones, needed LOTS of room. First off houseguests in those days stayed for MONTHS since transportation was so horrible. Secondly you have extended families (at least it would seem this was Joshua's intent) living under the same roof. Think of the wings as daughter in law houses and you get the picture.
Thirdly you have the need for TONS AND TONS of SERVANTS. Especially with a houseful of guests, the guests would be bringing along THEIR servants, as we see with Josette and Angelique. NOt to mention that in those days food preparation, housework and the other functions of running the house were done with people power not labor saving devices.