I am assuming that you are going to wait until next spring to start this project.
There are a couple f things worth mentioning here-
-the upper pond must be smaller than the lower (new addition) pond or you will have major water loss during periods of pump shut=down.
-no real need for an additional skimmer. Move the one you have. The cascade connecting the 2 ponds will "skim" the upper pond. This eliminates the need for an additional pump
-The need for a pond heater is a given, I guess, in your location.
I am sure that there are other Forum members that have 'hands on' experience with cold climate ponds that could offer advice. Rarely does anything really freeze in my area.