I didn't think it was really as bad as people made out, but I don't mind crowds. We just planned on not really doing more than our 3 FP at Epcot, but there's so much to do there that doesn't require an FP. The line for food and drinks can be long, so be patient. We bought some cushions earlier in the week from the store at The Seas to sit on while waiting for Illuminations. We don't normally bother waiting long, but we knew we would need to this time. We did make a dining reservation, which was good, since the lines for booths and QS were long.
MK on the 30th was great. Best fireworks I have ever seen. Most people were hanging out at the DJ in the hub later in the evening, so many rides weren't too bad. This was in 2016. The weather was a bit cold, so maybe the crowds were lower. They ran out of tea bags, hot chocolate, and coffee at MK but had plenty of hot water. Bring some tea bags if you think you would want a hot beverage in the cold. If you go in with patience and proper expectations, or maybe even over-expectations, then you will have a good time. I would do it again in a heartbeat if I get the chance.