For the most part - I agree with everyone else. I guess I would say there is a short list of must haves and an unending list of would be nice (lol).
My short list is lots of extra bobbins(my machine takes L size bobbins and I started with 12 which was not enough for me), thread (I too buy as needed), side grips/clamps and fabric to play with. I also purchased rulers and wish that I had waited - as after I was comfortable with the machine I purchased different ones from what I had. Also, if you are any where near a quilting show with classes it is an invaluable resource. Finally - several pieces of fabric (busy print and coordinating solids - i explain below).
A couple of books that were recommended to me were
ABCs of Longarm Quilting by Patricia C Barry
The Ultimate Guide to Longarm Machine Quilting by Linda Taylor
Both are excellent - the ABC one had some great beginner tips and a few easy projects. As my machine is not computer controlled - one of the best beginning tips I found in it was use a very busy print for the backing and a coordinating solid for the top. You can easily see the stitches on the plain - and even if your free motion is not perfect, the busy print hides the discrepancies. I did several of these and made sewing projects from the quilted pieces. This bag was the first project and the first piece of fabric I quilted. The pattern and directions were in the ABC book.
http://www.quiltingboard.com/picture...ag-t42132.html
The Linda Taylor one has lots of inspiring pictures as well as a section with full size designs to copy.
Good Luck!!