the nook tablet because its newer and it has more battery power and more for just 50 dollars more.
Well I think you can through your nook account if your nook is destroyed. Or do you mean let a friend borrow a book the answer is yes for most nook books.
no
The NookColor defeats the purpose of an e-reader. The Nook is supposed to help you with your eyes, by not looking at the bright screens.
Since it is android os, you can do just about anything with it. You can install customs ROMs and customize it to your liking. You can also read books.