At this point, we don't know when the Holiday season will official end, but my guess is that by the 11th/12th it will be over, so fireworks and F! will only be presented on Fri, Sat, and Sun. WoC is generally presented nightly. We don't yet know what PtN's non-peak season schedule will be.
In terms of the number of days, it depends on what you mean by "most things". The weekday operating hours tend to short (e.g., 10:00 am to 8:00 pm), but the crowds also tend to be somewhat lower. There is less entertainment offerings, so it means less things to try and see. I think you can get a fair amount accomplished in three days, but you will still probably have to skip some things due to time. (Note that if you do go right after the holiday season ends, there is a good chance HM will be closed to have the overlay removed. Other things may also be closed to have holiday decor removed. Jungle Cruise may be closed or not, depending on when they decide to remove the overaly. IaSW usually closes about when HM re-opens, so later in the month.)
