I would suggest you don't make it all about a 20 minute fireworks display. There is much more to a NYE holiday at Disney World. Stick with your plans as NYE is a crazy day at the parks and Epcot is the one park large enough to handle the massive crowds. We have gone to AK in the morning on the 31st as it will be the least crowded because it closes early, then hop to Epcot. Yes, hopping in the evening is easy enough as most come early believing the notion (not true) that the park will have a capacity closure. One caveat, Do Not Drive! I would suggest you get an Epcot resort to be able to walk back after!
As to your specific questions, have not read anything about NYE 2019 and possible changes.