I'd skip Echidna entirely unless you have SCs to spare for her, tbh. I've never deployed her since I got her. (Granted, I got Camilla and Chydis early...)

IMO, I'd prioritize first-copy Aria > Fleur > Dorania > mincosting Aria > farm silvers > Echidna > get another Dorania >>>>>>>>>>>>>>>> mincosting Echidna.