It seems you are looking for rigid body collisions.
1. This gets complicated real fast. Reading a book on physics is a good start but if you don't want to read a book you can take a look at this http://www.myphysicslab.com/collision.html
Just be avare that there are a lot of vector math and physics related terms and if you are not familiar with them this will propably not help you much.
3. As long as your objects arent bolted down to an axel then yes. Objects always rotate around their center of mass.
4. This one is also a lot of complicated math involving a lot of vectors. The link in #1 mostly covers this if you can read all the scientific terms and know vector math.
Seeing as you are only 14 my advice is to pay close attention in math and physics classes at school. It may sometimes seem boring but when you start to understand all of it and you get your first physics simulation program working it gets fun real fast.