Yes typically MK EEH are on Wednesday and Epcot are normally on Monday. Yes it is always fun and it is nice to not be in the hot sun. On these days we tend to take a longer break from the park after lunch and then are able to have extra energy to stay late to enjoy EEH.
Note that you can't use your LLMP and/or LLSP or even LLPP for EEH.
Crowds are lower since it it only open for Deluxe &
DVC resort guests. It tends to be busy right at switch over as the day guests are in the Standby Queue for one more ride. We tend to skip the fireworks on those evenings and hit our favorite rides while everyone is still watching the Fireworks.
Dave