As far as I am concerned about the extension of OPT, you can  apply three months before the expiration of your present OPT with the employment letter and the e-verification number of the company. Since you have the present OPT valid of one year, there won't be any problem working with in that period just for the extension you need to have the employment letter and the e-verification number of the company and you can file for extension with in the nine month from the date of the release of your present OPT.