Don't worry too much. First, windchill affects mainly living creatures, second bodies of water, and, dead last, solid objects. Its effect on your Leaf will be only to get it down to ambient faster, not below. I had my 2013 SV parked in the open, on the usually-downwind side of the Hudson River, with temps as low as -15F. I also used 120 volt charging only. Keep the state of charge above 40% as much as possible, and always above 30% when exposed to frigid temps, because the battery warmer will start when the car's pack temperature falls into the single digits. The warmer will use a noticeable but not huge amount of charge until the pack warms back into the teens F, IIRC. With your short commute you can charge the car to between 70% and 100% (80% would be best) and not worry. Your car can deal with your Winters better than with really Hot Summers.
Just as an extra precaution, don't leave the car plugged in but not charging unless the battery warmer is on. (This is indicated by one of the blue charging lights lighting up, IIRC.) Earlier versions of the Leaf could suffer from a drained 12 volt accessory battery if left plugged in but not charging for many hours or days. This has probably been resolved with the 2018, but that isn't a known fact, yet. You shouldn't need to charge the car for more than half the day, anyway.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.