It is very labor intensive, and takes practice to develop the "hand" for it.
George is right on about the templates.
You will need a heavy duty upholstery sewing machine. You also have to use stainless staples, and an air stapler. The staples on higher end jobs are literally a solid line of staples with no gaps between them. The molding material that hides the staple rows is called "Hidem" or "gimp".
is a good source for materials & tools.
It will take a while before you will want anyone to see your work, but it's nice to be able to repair and make things you need. I would choose something else for moonlight work, though. Way too many ways for customers to find things in your work they're not happy with - just ask my upholstery guy!