Just start your Mac holding Command, Option (Alt) and R keys, and reinstall OS X. Your Mac comes with OS X Recovery, so you don't need OS X Mountain Lion on a USB drive.

Instead, it would be much better to get an external drive. In the case of Macs, I don't recommend you to install a hard drive bigger than 2 TB in order to avoid some problems. Any 2'5' SATA hard drive will work with your MacBook Pro, and you have three hard drive types: a 5400 rpm HDD, a 7200 rpm HDD and a SSD, choosing the one you most like (if you haven't got enough money for a SSD, go for the 7200 rpm HDD). The following items are also compatible with this product. Respecting to the hard drive, you can upgrade it or install a SSD without voiding warranty. MacBookPro8,3 - A1297 - EMC 2564 Late 2011 17-inch : How to find Model ID Installation videos: Standard Memory: 4 GB: Maximum Memory: 16 GB: Note: 4 GB of RAM is installed as two 2 GB modules, no slots free. You can buy more memory from OWC or Crucial. In fact, the 2011 MacBook Pro supports 16 GB of RAM.

Ram memory for macbook pro late 2011