You will love it!! We had EMH on a party day and there were only a few dozen people right in front of the castle to watch the welcome show at 7:55. (Though, certainly more people were around through mainstreet &/or already lined up waiting to be released to where they were headed first). The first 2 hours were just so magical with how low the crowds were and the rest of the day wasn't too bad, either. We had planned our first few hours to hit up rides via stand-by and then starting around 10:30am we had our FP+s and ADR. We left around 4pm, took a break, and park hopped to Epcot. (We attended
MNSSHP a different night).
With rope dropping and strategic FP+ and ADR, we didn't have any crowd issues at the other parks, either. It's not that it wasn't busy (it was), it was just that we had a plan and were able to accomplish what we wanted to without the crowds feeling oppressive.
There were major crowd issues at MK on the evenings of non-party days, though. That was bananas and not fun. Thankfully, one night was our arrival day and our only goal was a walk-up dinner and to use 3 FP+ and then leave. And the other MK night, we were content to watch fireworks while riding Barnstormer on repeat.