This calculator I’ve posted previously will tell you what your approximate cooling requirements will be. You want the “Cryo” tab.
https://drive.google.com/open?id=1IOTKDyLu3lmWqnNgrOjpZUZNUFqjIwSQ
Put your ethanol volume (in liters) in the first highlighted box. Initial temperature in the second, final temp in the third. Number of hours you want to chill it over goes in the last one.
The boxes below give you approximate values for total energy required. This is an average over the whole temperature range and not actually the number you should use when sizing your units.
I’m a fan of CryoDax units, so when you put the volume in the first box it will also tell you how long it would take each of their units to chill that much in the rows on the bottom left.