Monochromatic is so hip and yellow is a beautiful choice. You should do another accent color and have the bridesmaids carry those bouquets instead - fuschia looks amazing in photos and is a very fresh spring color as well. You might also want to go with tulips rather than calalilies. They are less expensive and looks just as pretty...a little softer and would look fantastic with roses. Eitherway, if it's something you envisioned, it will be lovely and if you go with something else you'll probably end up second guessing it the whole time anyway.

Good luck with your planning!