I would recommend booking as soon as possible. Rooms at the CR seem to sell out very quickly. Part of it has to do with it being a convention hotel, I'm sure. Have you checked availability for your dates online on the WDW site? That would give you a good idea on what's still left to book.
If you don't find what you want, don't give up. Rooms do open up. We wanted the tower for our September trip and there was no availability for the last two days of our trip in anything but a suite.

I checked the site daily starting in January, and finally last week a whole bunch of room types opened up and we were able to get the room we wanted.
I do think that the garden wing rooms go quickly because they're the least expensive. I noticed that none of those rooms have come available for our trip dates at all.