Usually, the first week of May is relatively moderate. There might be crowds for some things and not for others. For example, when I went last year, BTMR and Splash had wait times of 45 minutes, where as Space Mountain had a wait time of about 5 minutes. However, with the celebration starting this month...I would assume that the crowds would increase just a little, since a lot of people are going to try to catch this event when it starts. The other thing to take into account is that a lot of people will still be in school at that time, so a lot of families won't be there yet. Basically if it is extremely crowded take advantage of FastPass and if staying on property, Extra Magic Hours.
As for your question mangosink, I don't think that Cinderellabration is going to cause a huge influx in May crowds simply b/c it starts today (I believe) so the majority of the people who are locals will be going as soon as possible, so the only thing that will cause an influx of people will be the ones who want to experience the whole Happiest Celebration on Earth.