Welcome to the CADTutor forum JSM.
Take a ride down to your local bookstore and buy a copy of AutoCAD 2009 / AutoCAD LT 2009 No Experience Required. The book was written by someone with an architectural background and takes one through all the steps needed to create a set of plans for a small cabin.
My personal opinion would be that yes, currently, most floor plans are drawn in 2D but that doesn't mean they couldn't be done in 3D.
Layers should ALWAYS be used in any type of drawing as it leads to better organization and less clutter.