You can book up to 7 nights at 11 months from date of arrival at your home resort and 7 months from date of arrival at another
DVC resort. So if using 7 month window, on December 14, 2014, you can book July 14 to 21, 2015 or anytime before that if still open.
Also, your use year determines points applicable to a trip but is irrelevant to when you can call to reserve, which is always up to 11 months out at home resort or 7 at others. Thus, with Dec use year, you could today, Sep 24, reserve a trip starting Aug 24, 2015 or before at home resort or April 24, 2015 or before at other DVC resorts and use those points that would be in your Dec 2014-2015 use year which would be your "current" use year points for that trip.
VGC can often be found available at 7 months out between second week of Jan and the Friday before Memorial Day weekend in May, except for holiday periods during that time. From Sep to before Christmas it can be hit or miss at 7 months out, except holiday times are usually quite difficult. Unlike WDW, first half of Dec is actually one of the periods you can usually get VGC
At WDW, you have basically two seasons:
(a) low to moderate demand season when it is easy to find many things even at near park resorts at 7 months out, which runs from the Monday after Marathon weekend in Jan through the third week of Sep (and that includes holidays, e.g., you can get BLT lake view and BWV pool/garden view during Easter and July 4 time); the main exception during that time is the Princess half marathon weekend in the third week of Feb when near park resorts have a real risk of filling before 7 months out;
(b) high to extremely high demand season, when it can be difficult to impossible to get near park resorts at 7 months out, which runs from late Sep through marathon weekend in Jan; during the extremely high demand times -- first two weeks of Dec, Christmas week, Thanksgiving time, second weekend in Nov, and the Thurs before Columbus Day through the Monday, a week after Columbus Day-- even AKV and OKW face some risk of being unavailable at 7 months out for some days during those times; there are three moderate times during that quarter when chances are very good even for near park resorts: mid-Nov to Friday before Thanksgiving, third week of Dec, and time between Jan 3 and the Thurs before Marathon weekend.