stop trying to complete nightmare campaign. there's really never a reason to grind on nightmare campaign, so it's just a one-and-done type deal. focus on other areas of the game that are important for advancement and come back to clear nightmare down the road when your account is stronger.
in the same vein, i'm not sure you should be worrying about hydra at the moment. you certainly have some champions that are useful, but there are too many specific abilities you don't have an answer for. just as an example, you need either aoe hp burn or aoe block debuffs to counter the head of blight's poison cloud and i dont see either one in your collection.
in terms of food, just about every rare that you have can be turned into fodder. apothecary, reliquary tender, and renegade are all definitely worth saving and i'd sugegst keeping frozen banshee and dilgol at least for the moment. the rest, along with any uncommons and commons (except for armiger) are all food.
i agree that apothecary is an excellent candidate for 6 starring, and i'd recommend toragi as well.