1. Yes, some people dont like to but it will not stress the animals
2. it depends on the wattage, i would say a 75w will get the job done, depending on what you keep the house temps at
3. as long as it is hot enough then you will be fine, the chances of an impaction does go up a little but as long as you are doing everything else right (food size, substrate, etc...) then you will be fine