Heidi,
Ray's suggestions on the siding are right on. Follow his cautions carefully.
2 x 6 studding lends itself to blown in cellulose insulation which lasts a very long time and makes for an air tight house if applied properly. Don't forget to use low expansion foam around all the window/door jams before you apply the dry wall. Your insulation contractor can give you the R numbers for 2x6 studding. It varies by density of the applied product.
Big caution. Use a closed cell foam air damn underneath the sill plate, the black stuff, NOT the cheap blue stuff.
Next question ?
deralte