Welcome to the forum! This is an awesome place to be. You will learn a lot!
To answer your questions...
The OG is an excellent resource. It's a must-use book. The tests are paper tests, not computer-adaptive ones, so the score won't be overly helpful. However, the questions are great practice, so definitely use this book. Take the GMATPrep official practice tests. There are two and they're free; you download the software from http://www.mba.com
Also use your PR book for strategy and take those tests too. The PR tests are very close to the real thing. I like the answer explanations also.
A couple of hours a day for studying is a good plan. Do practice questions on weeknights, one question type at a time until you've gotten into a good groove for at least 10 minutes. (i.e. you might work at it for 20 minutes and then it kicks in and you're cruising and getting them right, so keep at it for another 10 minutes at least.)
Do a full practice test each weekend and carefully review your answers. Are you getting the same question types right/wrong in practice and on the tests? Use that review to finetune your plan...whether you need to work on fundamentals (same question types wrong on tests and in practice) or timing (right in practice, wrong on the timed test).
I would not take a test at a test center as a practice...it is definitely a waste of money and pointless to do without seeing your score. And if you see your score, so do any schools you send any score reports to. If you want to take a proctored test to see what it feels like, go to one of the free diagnostics that Princeton Review or Kaplan
offers. (Although I'd do the PR one over Kaplan
's tests are much harder than the real thing, so it's not a good gauge.)
btw two good resources for info about the application process are http://www.businessweek.com
. I'm on those sites all the time. review.com has a good amount of articles. Plus you can get books about applying to b-school, with more detailed info.
Hope this helps!