I'm currently working on another picture book project. Now, that the first draft is done, I'm in the revision stage and really trying to look at the manuscript visually and envision what text can, if (and should) be replaced by illustrations. I found several pages where illustrations can very easily, and perhaps more engagingly, show what the words are telling the readers. This requires the use of illustration notes, otherwise the text doesn't make much sense. I've heard conflicting opinions about authors using illustration notes in the manuscript, but I've found a very helpful post on this subject, so check it out and let me know your thoughts or experience on illustration notes.
From what I gather, the consensus seems to be: use illustration notes if you need to, but use it sparingly.