Orbs spending

I finally summon b Cordelia +hp/-res (still i wonder It there is any some special precation for her like Better moonbow or luna and If is Better threaded def or Speed) the question is: should try to make the obtain the most orbs as possible and try to summon to try to get Charlotte or caeda since i do not have nor effie nor blue mage (since they are good limited), try summons tharja but i still have lucina or Just Save them for the sick of It?