Hi Prasannathawait,
Raising a 320 to a 500 is a significant achievement, so you clearly have the ability to learn and improve. In a prior post, you stated that your Score Goal was 700+; if that is still your Goal, then you still have a lot of work to do. Raising a 500 to the point that you can consistently score 700+ will likely require at least another 3 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Thankfully, the GMAT is a consistent, predictable Exam, so you CAN train to score at a higher level.
You also stated that you planned to take the GMAT in January. While there's no real 'harm' in taking the GMAT at that time, it is unlikely that you'll improve another 200 points in less than 1 month. Thus, you can save some time, money and aggravation by pushing back your Test Date.
1) What are the application deadlines for the Schools that you are considering? Are there later application Rounds (and if so, then what are they?)?
GMAT assassins aren't born, they're made,
Rich