Good questions.
You can draw anything you like since the GameCanvas has a paint(Graphics g) method it inherits from Canvas.
I believe for the Tiles you put then all in one file, and then it gets layed out. The Tiles are always in the background.
Here are a bunch of technical articles at Sun's website, check near the bottom.
This one in the list is specific about the GameCanvas and stuff.
On the Book side Jonathan Knudsen's J2ME book is my favorite. Carol Hamer's J2ME Games book is also a very good reference. Both are published by Apress.
Good Luck
Mark