1 - Is it even safe for the plants/animals to use a container that once housed rodents?
should be just fine: bleach it good if your worried and then rinse it super well.
2 - I understand that, in the absence of drainage holes, there needs to be something under the dirt for the water to drain into. Would a half inch of gravel do the job?
if your going just gravel i would add more than a half inch. you don't want your soil in contact with the water. I like the false bottom personally and would go that route. a 1-2 inch false bottom and then your substrate layers (which in my viv consists of .5 inch of eco complete or gravel and then ABG mix)
3 - For soil, would simple, plain top soil work?
No. potting soil will not stand the test of time, get compact, and not drain well. Go with a good ABG mix and your good to go. there are a lot of discussions on the right mix and some folks make some great ones. but in my opinion, the original ABG is simple and pretty darn good for most scenarios.
4 - A lot of animals that could work for such a terrarium need live foods. Do any such foods exist that (A) are easy to culture, and (B) are not likely to infest the house?
everyone has their own def of easy, IMO well fed and dusted crickets can make a fairly easy, staple diet for most herps. depending on where you live they are cheap and easy to get. culturing can be messy and smelly
5 - Speaking of which, any animals that would work well in such a setup? (It would be nice if the creatures were attractive and not outrageously hard to breed)
this might be a giant discussion all on its own!!! good luck and keep us posted!
Thankx in advance