Annual passes do not go on a calendar year, they are valid for 365 days after you activate them, no matter when in the year this is.
There are many discounts associated with being an annual pass holder. There are frequent hotel discounts and fee reductions at some restaurants, shops and recreation opportunities throughout the year. The best way to find out about specific benefits would be to call the
annual pass office directly. The number there is 407-560-PASS. The cast
members there can give you all the details.
In doing lots of research, I found that in order to take advantage of the Free Dining promotion, you need to purchase a stay at a WDW hotel room AND at least one day of park tickets. The annual pass alone won't do it. However, if you hang onto those park tickets and don't use them, you can then apply the cost of those tickets to the renewal price of your next annual pass. It is slightly complicated, but I did read several accounts online where this worked for guests.
Just in case you weren't aware, I have found the very best benefit of being an annual pass holder is the ability to purchase the Tables in Wonderland card. You can read more about this
HERE and
HERE.