I am probably the last quilter in the world who has never done a disappearing 4- or 9-patch so can't help directly with that.
If you are following regular instructions (as opposed to what I often do which is make things to the size of my scraps) there is probably somewhere a finished top size.
A lot of people make crib/baby blankets roughly 3x4 feet. I cannot seem to make a quilt smaller than 40" to save my life and it's hard for me to make a quilt small enough to fit within one width of fabric.
If you are going to start making these for donations (or just have a lot of babies to gift!) I would indeed just make the first one and go from there. Good luck with your projects.