Hi,

1) Is the OG 11 enough to study or do I need to buy the OG 12?

Yes OG11 is more than enough. See to that you practice a lot with OG (esp. verbal). Og12 only has a few new questions in each section and rest are repeated from previous versions of OG. So, OG11 alone is enough.

2) I am planning to study the OG 11 and Princeton review problems. Is this enough or should I get more books?

Can you be more specific on which Princeton Review book you are using? For Math, i don't think this is enough. You need some more books for practice. Books such as OG Quantitative review 2nd edition OR Kaplan Advanced would do.

3) Do I need the MGMAT books?

Well, how good are you in basics? If you are not pretty good in basics, i would suggest you to buy MGMAT all quant books (5). They cover pretty well in foundations. Or, you could even go for Kaplan Math Workbook if you feel that MGMAT books are expensive.

For verbal, you have to study the strategies even if you are good. For Sentence correction, i would recommend MGMAT sentence correction 4th edition guide. For Critical reasoning, get Powerscore CR bible. For reading comprehension, you can takeaway strategies of CR and practice more with OG. Also, read sites like economist.com, sciencedaily.com to improve your reading comprehension skills.

4) What is the best way to study for the test from now until June?

You have ample time to study. Firstly, spend some time with basics. Working with basics is the key for success in GMAT. Don't hurry up in skimming thru basics. Don't work out GMAT problems until you are comfortable with basics. While preparing for basics, practice some problems to apply your basics and test yourself.

As an aside, take a diagnostic test in OG11 to see where you stand. This will help you assess where you are and you could devise a better study method based on your performance.