Marr should be maxed ASAP. Other healers can be leveled afterwards. I'd personally prioritize Iris > Alissa > Fedora, in that order.
Khuri is also worth maxing. After that, a mincost silver archer (probably Daniela, since you have more dupes of her lying around) will be good.
You might want a cannoneer sooner rather than later.
Pallis should be CC'd, she's pretty much superior to Valerie.
If you haven't already, CC a second Calliope and CR them as much as possible. I'm assuming you haven't cleared War of Magic yet.
Heavies should be maxed. Garrett won't replace Leeanne, but you can probably try using him over Bernard.
Lilia/Claudia and maybe Rika will probably be your best duelists. Lilia is at a decent level for now, so I'd get Claudia up to her level. Rika should at least be CC'd. If you need a cheaper duelist, work on Eunice.
Rogues can be mostly ignored. If you need a dodgetank, you could try CC'ing Cypria, at least.
tl;dr: I'd work on Marr >>>> Iris > Alissa > Khuri > get Percis > CC Pallis > witches > max heavies > max duelists