I want to put an addition onto our house which will completely extend one side of our home to enlarge the upstairs bedrooms, main level living and dining rooms, and downstairs basement. Where in the world do we begin? (I am extremely handy - can do almost anything - and have a repair/remodeling business on the side)

If you're in a place that requires a permit (most people are) you'll have to start with a formal plan. Then get a permit.
As to how to actually do the job.. I suggest you start at the library.