You can make your reservation and lock in your room only price up to 500 days in advance by calling WDW. Your room rate will be locked in and they won't change it UNLESS you change the details of your reservation. If you look at adding any type of package, room discount or change your room type you will be adjusted to the current prices based on when you change your reservation. If you book your room then buy tickets or AP's without a package and pay OOP for dining your original room price is safe.
As an example I booked package a few years back in Jan or Feb for a Oct trip. A couple of moths later, after the spring price increase, I called to have a promo added to my reservation and my over all package price went up by about $50-$100! Basically I was adding a Room discount of 20% but the overall package was being updated to current prices and tickets, room, and dining plan all went up 5-10% since I originally made my reservation and it netted out to a overall package price increase. Needless to say I said never mind the discount and stayed with the original prices.