RE: looking to build a base and habitat
To make the dirt, all you need is to mix Elmers glue, dirt and a little water and some salt.
Mix it together and make a mud. Wear gloves!!!
Spread it out on a piece of ply wood only about an inch or so deep.
This will take several weeks to totally dry. The salt is supposed to help prevent mold from forming.
You can also coat leaves with a mixture of 50/50 Elmers glue and water. Dip the leaves in the mixture and allow them to dry. This coating will help preserve them but won't preserve the color.
Add a few small twigs, acorns and what not.