1) Is the IR section and the Argument essay taken into account for the final score. Even though I didn't get any IR questions correct I still got a decent overall score.
No. The score you get out of 800 does not include Essay/IR score. You get separate scores for both these.
2) My overall target is to get a 700+ and am wondering if this would be a realistic goal if I plan to study on average 20hrs/week for the next 3 months before giving the actual GMAT
It is realistic but you will need to work hard. It depends a lot on how fast you catch up, whether you are conceptually strong but rusty or weak in your basics etc. Your score could shoot up in a month's time or it could take quite a while but the expectation of 50 points per month increase is definitely fine.
3) What would be a best resources besides the official 13th edition guide (which I do have) to improve upon my scoring
You might want to get a full set of prep material before you dig into the OG. Get your basics right and then practice from OG. Check out our offerings here: http://www.veritasprep.com/gmat/
4) How much more can I improve on my verbal if my mother tongue is not English but I studied in a school with English as a teaching language and have been in the US for the past 13yrs
If you have been living in the US for the past 13 yrs, your English would be as good as your mother tongue now. This means that people living in US do not have an edge over you in Verbal even though their mother tongue is English. But then, there is a big gap between speaking English fluently and Verbal section of GMAT (this is the reason that all English-speaking people do not get 51 in Verbal). How much more can you improve? You know that V51 is the limit.
5) Why is my verbal percentile higher compared to quant even though the quant score is higher than verbal
There are many more people scoring in the 40s in Quant than in Verbal. Percentile is all about relative performance.
I am definitely not happy with my IR performance. So will be focusing on it very heavily but if its not taken into account should I worry about its score for the actual GMAT. The scoring table given at the back of the official guide only shows a calculation for the Quant/Verbal and Overall scores.
Yes, work hard on IR and the other sections too.
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