ok- first question--pre-washing- you will get about an equal amount of answeres for both sides- there are folks who pre-wash every single fabric- (precuts are a bit tricky- some people do them by hand- some place them into a mesh laundry bag) and there are folks who never prewash any of their fabrics- and there are some (like me) who prewash some ((if i am worried about a color bleeding- or excessive shrinkage- or if the fabric smells or feels weird) but i never pre-wash pre-cuts...it's your choice- just remember- if you prewash your precuts they will not measure the same as when they were new- patterns will need to be adjusted-
now as for batting-
my choice for your North Dakota bound would be Wool Batting! i love Wool batts!!! they are lightweight- lofty- warm in the winter & cool in the summer- the quilt that lives on my bed has a wool batt & it is wonderful- summer & winter! to add weight/warmth (if you are making separate seasonal quilts) you could use a wool and a cotton batt together---many quilters double up their batts.
polyester batts can be quite warm---since they don't breath-
if i wanted to make a heavy-warm quilt i would probaby use flannel, corduroy or denim for the back (or fleece/minkie---which is amazingly warm & snuggly) a quilt with a warm & natural cotton batting and a fleece backing will keep the coldest person warm!