I felt Cracking covered all the topics you needed. If you want to study beyond that, it would probably be useful to spend time going through the stuff covered additional topics section in greater detail, like get a textbook on abstract algebra and probability theory and complex analysis and such.
The GRE on the ETS website is a real GRE which was actually administered a couple of years ago, so it should be close (there are actually 4 real GREs in circulation, make sure you collect them all!). However, most people on this forum, myself included, feel that when they actually took it, it was much harder than what they had expected from those GREs. Not that the questions individually are harder, but there are simply more questions of the difficulty of the hardest questions on the old ones. Because of this, timing could be an issue, as if you are expecting a certain time per question from the practice GREs, you will be surprised on the real thing when it takes you longer to answer most questions. I would go so far as to suggest that you give yourself less time on the practice tests than you'll have on the GRE.
They will mail you the results about 6 weeks after you take the test, but you can call them and pay to get your scores like a week before that (which begs the question why they have your scores and aren't sending them, actually from the website debacle last year, we know that the tests are actually scored by about 2 weeks after the test is administered, for a short while if you checked the ETS website at that time, you could see your scores).