Am I correct in thinking that the auduino can be powered fromn the usb bus?
Yes it can, but if you are powering it from the bus then you can also get the USB connection to carry the MIDI data.
It seems to me that all I need to change is analog cc no's?
In effect yes but:-
Is it really that simple?
While a cut and paste approach repeating sections of code will work it is very turgid and difficult to follow. You will do well to learn a bit about arrays and for loops to make your code much much shorter.
a complete beginner and having no prior knowledge would it be suitable?
While initially a lot of it might seem over your head when you first pick it up their is an introductory chapter that tells you about schematics and how to wire things up. The projects range from the very simple to the very complex so their is a lot of growing room in the book, as my mum used to say when she got me jackets much too big for me. 