-Generally speaking, when it may, does a 'Carnivore' attack another species for a subtraction of 1 in it's population per copy of the Carnivore card? If the carnivore wants to subtract 2 population, does it need 2 copies of the 'Carnivore' trait to do so?Species can never have more than one of a given trait. If a species is a carnivore, it has one and only one carnivore card, and each attack always and only decreases one population.
-Do Carnivore meat tokens get turned the other way around from tokens in the watering hole, or do the meat tokens come from the food bank , prior to the waterhole?Food for carnivores is taken directly from the food bank, not the watering hole. Carnivores can never take food from the watering hole, since all food in the watering hole is by definition plant food.
-Is there a limit to the maximum number of cards permitted in a player's hand?Not particularly, no; though if you hang on to too many cards, you're likely going to fall behind (possibly unrecoverably) because other players are using their cards to do things -- especially creating new species (which allows them to draw more cards).
-Are there going to be any of the edition 1 cards re-done and included in edition 2, like omnivore, swimming (aquatic, which may include a custom attribute card and template), hibernate, or for example more new ones, eg. enhanced hearing?What "edition 2" are you talking about? There is a second edition already, and it just has some minor balance reworking (like hard shell being +4 instead of +3, and pack hunting being +population instead of +3).
For reference, all non-carnivores are considered omnivores, so there will be no such trait (if a carnivore with cooperation passes food to a non-carnivore, that food is technically meat; same if a non-carnivore has scavenger -- the food they get is still meat).