To Netti, the OP-
Although you have only a short time to book your vacation, you can do all the research a head of time. You can decide what character meals, reasearch restaurants for ADRs, research resorts, see if there is a special event going on, make a must sees/do list, etc. We always make a list of the top 3 character meals we want to do, then pick 2. We also do this for restaurants. The extra is a just in case we can't do this one sort of thing. This way you'll be prepared and once you set your dates, you can call and make all your ADR ahead of time. I also check parade times, park hours, shows, refurbishments etc. monthly. I do this for no more than 15 minutes and keep a running binder with pocket folders. Things change and something is always added and taken away. I also look at last year's month (So we looked at Dec. 2005 to get ideas about this year Dec. 2006). Once we're booked, it takes me 10 minutes to put it all together. I find when you have a lot of time to book, you change your mind again and again. Last year we went with less than a month's notice and got to do everything we wanted. We went during an off time in late Sept., but we got it all. We even got our Magical Express tickets with 5 days to spare.
Since you think you're going in May, definitely do some research now.
I hope this helps.