Whew, lots of questions! Sounds familiar, I was in the same position a few months ago.
I would give a diagnostic test to begin with. Maybe the OG paper test. That will highlight your weaknesses and you can begin working on them.
OG 10thEd is useful, but I recommend you buy the 11th Ed also. Personally I have not done a comparison even though I own both. But I have seen this suggestion in several forums. I did not use the Verbal or Quant GMAC guides but knowing the OG, I think they will be better than say Kaplan Verbal. I do have suggestions for specific topics in my de-briefing above. And the GMAT 800 is indeed the Kaplan 800.
You can get GMATPrep from mba.com (preparing for GMAT section). PowerPrep is the older version of GMATPrep, and you might be able to find it through google.
I did not use any maths book. Most guides have good summaries. The 4gmat.com guides are worth a try. They are just 8 bucks each.
You can find several good posts for AWA in this forum. Just do a quick search. I picked up most of my cues from the OG and tried to keep the essays simple and structured. Three points, one example, short sentences, minimum repetition, nothing fancy.
Needless to say, these pointers may or may not work for you. Read a lot of different posts. There are certain definites like OG or "the need to review all questions" that you should not doubt. But you will have to find your own sweet spot for things like error logs, AWA template, study schedule, flash cards etc.
Best of luck.