Those are legitimate questions. Here's what I'm sure of:
Genesis 1:24 tells us that God's planned for the animals to reproduce. Genesis 1:28 tells us that God planned for humans to reproduce.
Genesis 1:29-30 says that God gave plants and fruit bearing trees to humans and animals for food.

Here's what I deduce (my own personal opinion):
I have no idea what God's plan for population control was had sin never entered the world.

I believe that either God created man and animal with the physical characteristics needed for a carnivorous diet (if you listen to some vegetarians they'll say that man doesn't have carnivorous teeth now), or that the physical characteristics needed for the carnivorous diet came about through micro evolution. I think it's possible that Cain and his descendants might have been the first people to eat animals based on the curse God placed on him because he killed his brother. Genesis 4:12 tells us that part of his curse was that the ground would no longer yield good crops for Cain. It also says that he would be a homeless wanderer which tells me he would not have a place to establish a farm on which to grow crops.

I'm no theologian, and these definitely aren't Heaven and Hell issues, but they're fun to discuss, ponder, and hear the different ideas others have based on their reading of the same text.