The crowd ranking does not equal a wait time. It is safe to assume that the lower the crowd ranking, the easier it is to get on the rides b/c there are just less people to deal with. My DH and I traveled to WDW when it was a level 3, and we walked on almost all the rides. But we still had to wait for Peter Pan - 50 mins every time we tried - and Toy Story Mania - only got to ride twice - once we waited in line for 45 mins and got a fast pass for the 2nd time.
At the beginning of May, you are pretty good. School is still in session and Spring Breaks are over. So it is a good time to go.