I agree that the less time you have, the more you have to prioritize. The more time you have the less you have to because you have so much time to fit everything in.
that said a few things to keep in mind (of course IMO):
1) this is a relatively quiet time of year. Now when I went in September 2014 it was also supposed to be a quiet time of year and there were a lot more people around than I expected. that said even though it felt more crowded than in years past, it was entirely manageable with fastpasses for the attractions that have long lines and all of the attractions that only really have lines when the park is packed. I expect it will be similar in december.
2) I never did an EMH either early or late on my last trip and we did most of what we wanted to do in Saturday to Saturday that included Saturday as a travel day, 1 full day not at the park (KSC) and 1 day for disney springs/rest/pool. I think I had 5 day non parkhoppers and we did one half day at AK with
MNSSHP one night, one day each at Epcot and HS and 2 days at MK. This time I have multiple days planned at both Epcot and MK and have parkhoppers so are splitting things up a little different (doing different nighttime shows than daytime activities and doing more TS meals).
3) we were flexible about what we wanted to do. Rode 7DMT once and one and done was fine. Did toy story mania once. did things like tomorrowland transit authority multiple times. Basically being willing to do less popular attractions and shows to fill in times when the other stuff is more crowded led to really nice days. Not being so focused on "e-ticket" attractions with huge waits just made it so much more enjoyable. In a less busy time of year the less popular attractions will have little to no wait even on crowded park days.
I am kind of a zilla (like bridezilla lol) when it comes to planning but my method is to have everything VERY planned out and then be flexible and make changes on the fly day of. I had my phone out a bunch of times to switch fastpasses around a bit too and that is really really helpful to be able to do on the fly.