Many of your battery questions are debated.
What I recollect:
Recharging/topping off after short trips is good. Letting it go down to 20% on purpose is not so helpful. But, charging to 100% is not so great either. If you charge in "standard mode" (instead of range mode) then it doesn't fill to 100% so you are in good shape.
So, basically - leave it plugged in whenever possible in a "standard mode" charge. "Range mode" or "Performance mode" should be saved for special occasions, and it is best to time it so you use the car right after one of those "full" charges. Also, best not to do "Range mode" or "Performance mode" charges on a really hot day.
There really is little/no "memory effect" so letting the pack run down by missing charging opportunities isn't really useful.
Charging from 120V is somewhat wasteful as a relatively higher percentage of the electricity is used running accesories and charging equipment and less makes it into the battery pack than you would get if using 240V.