What is a diorama?
A diorama, in basic definition, replicates a scene, event, or moment, in a three-dimensional display. Basically, it is a picture, just it has actual depth, you can reach into it, and you can rearrange its inhabitants to suit how you intend to portray the story.
How long have you been in this hobby?
About 3 Years now.
My usual basis is nothing more than Styrofoam. However, I use other materials such as clay. Paints are simply various dollar paints from any arts and crafts store.