1) i would stick with newspaper if your keeping everything simple- just out with the old, in with the new

2) for heating, i would stick with 1 pad covering 1/3 of the tub. Be sure it is controlled by something- i would recommend spending more up front (if you can) and pick up a good thermostat like a Helix or Herpstat. I think it saves trouble in the long run.

3) I have no direct experience with gerbils as food, but i have read that they are more of a last resort for unresponsive snakes. I don't know if its impossible to switch back to rats, but it can be a pain.