Our place is pretty modest. It's just a wee bit under 1,200 sqft with a full 8' basement. It was adequate for a family of four and a bit more than what we need now that the boys are grown and it's just my wife and myself.
We've got about 1 1/2 acres. Location is in one of the more desirable parts of town.
It varies here. The houses that are only used seasonally can run a bit big but the year round places are smaller and more energy efficient. The cost to build new runs around 500.00$/sqft and the minimum lot size is one acre.
My retirement strategy is to own everything outright within a few years. You don't really hit your stride till you're debt free.