Who to max out really depends on the fairies you get. Are you able to regluarly get black ones? Because otherwise i'd put higher prio on Gellius, Odette and Lilia. Platinum fairies are a lot more easy to come by than blacks for me at least, so i have tons of armours to spare but not enough spirits. Not sure about your situation.
As for Cellia i think she really should be among the first ones after seeing what you have maxed. Her passive grants 3% more chance to get fairies on maps that drop them and it is increased to 5% once she awakens when we do get it. She also comes with her defense-for-all skill which can be useful at times. Of course, if you feel this is insignificant, go for Horace or Saki instead.
And yes i do agree that if you have those units maxed, Lynn and Ada can wait a bit longer.
Lastly, regarding Uzume, she will most likely be more and more important as time goes. Don't underestimate a 10% increase to all your units damage.