I would go against what sora said and not level your lvl 50CC50 plats even more, level 50 really is the limit where the exp and gold are needed en masse. You want to use platinum armours with 3x spirits of the same rarity for those. The exp gained from the standard fodders could be used to level your pre-50 units a lot higher than they would benefit the post-50 units.
That said, since you have Kerry, Nanaly and Spica at max already i would say...
1. Horace - She is a good unit to have both as an additional soaker and due to her ranged attacks.
2. Uzume - No i am not joking, you have a GREAT lineup already so add her skill into the mix and ditch Sakuya.
3. Lynn/Ada - I have no idea what other units you have, but you seem to lack proper early rush stoppers, they will be useful in some missions
4. Cellia - Her passive is great, and since your team looks rather solid i would prepare her for awakening by maxing her out.
5. Bernice, Lynn or Ada - Bernice is great to have another perma-tank as opposed to Maribel, while leveling another rush stopper is rather nice too.
6. Bashira - Because catgirl.
Aside from these, i would level certain units with plat armours:
Gellius > Odette > Karma = Lilia > Maribel
You want a maxed out tank and Gellius is incredibly solid. Likewise Odette will be a good mage to have maxed and it does not hurt to have a maxed out plat magic soaker like Lilia either.
Now, if you did heed my advice for normal fodder, you CAN also just max out Gellius and Odette and then save all the other armours + spirits for Cellia since she more or less equals Lilia and will be great to awaken for an increased passive at that.