Good to see you're interested in AM! Here's some answers:
1. You can import poly models as props. This means they exist within AM, but you can't animate/change them at the vertex/cp level. However, you could animate the car moving very easily.
2. There are some usable AM car models on the cd. Whether you can easily model a car depends on your skill level. AM is a spline based 3D modeller and so it differs from other poly modellers. Once you get the hang of it, it should be easy.
3. Yes, you can do this with a camera rotosope. However, a compositor would naturally give you more control.
4. Yes if the models are .mdl type.
5. Again yes if it's a .mdl.
6. Yes. AM also has a net render module.
Most of the work done in AM is "cartoony" because that seems to be what the average AM user likes. But that doesn't mean you can't produce realistic animations. Indeed there are plenty if you look hard enough.
Hope to see you again!