Lots of questions...I'll try to help and hopefully others will chime in too.
1) Whether a course would be better for you depends on you...your learning style (better with an instructor or on your own), your self-discipline (can you stick to a study schedule without homework assignments due? this can be tough because the GMAT's not exactly fun), etc. Take at least one practice test and start studying to see what your weaknesses are before deciding. There's no generic answer as to whether a course is right for you. If you take one, I would suggest Princeton Review...excellent strategies and practice tests, and they use the Official Guide for homework assignments.
2) I have not taken the new GMAT, but there's info on it on http://www.mba.com
. There are some interface differences from the old one, but not so major that it will hurt you if you practice with 2005 tests (including Powerprep, the previous official tests put out by ETS).
3) Highly recommended are the Official Guide, GMATPrep (the new official practice tests), and Cracking the GMAT
. The OG has over 1000 practice questions. I would consider all of these a must.
4) 2006 or 2005 books should be fine. I wouldn't go older than 2004 because the test has gotten harder in the last few years (GMAC is somewhat sadistic!!).
5) Five months is more than enough, and unless you end up taking a prep course after doing a few months of prep, could be overkill. Plus you could also run out of decent practice materials. Pace yourself so you don't burn out. If you find yourself doing better than expected in practice, just schedule your test. Don't schedule it, though, before you start prepping, so you can get a feel for how much you really need.
6) Plan on doing practice questions on weekdays, focusing on one question type at a time, and keep an error log
. Do a full practice test on weekends, and time yourself. Try to mimic test conditions...keep it quiet, distraction-free, and stick to the break limit. Build up your stamina, and eat well, especially before taking the tests. The more comfortable you are with the whole process, the more relaxed you'll be on test day.
And no matter what anyone tells you about chugging Red Bull or taking ADHD meds to boost your concentration or energy, DON'T do it. Don't do any major diet or other changes just before your test.
Hope that helps...welcome to the forum!