For future reference...the best way to refer to your computer model (so that we understand what it is)...it's a:
15" Core i7 2.3ghz retina-MacBook Pro.
It would be best to enter this info into your Mac-Forums profile...then we will always know what you have...and then you won't have to type this info over & over when you have questions.
First let me mention that since this is a retina MacBook Pro (no optical drive)...your upgrade options are much more limited than with the non-retina MacBook Pro's.
Regarding ram upgrades (which you didn't exactly ask about)...you cannot upgrade the ram on this computer. So if at some point in the next 5 years you find you need more ram...there's not much you can do about it.
As far as the hard drive/storage capacity upgrades. In non-retina MacBook Pro's (with an optical drive/CD drive)...you can remove the CD drive...and install a 2nd storage device (an SSD or a hard drive). With the retina MacBook Pro's you cannot do this...since there is no CD drive to remove to make room for a 2nd storage device.
Your retina-MacBook Pro came with 512gig of "flash storage".
Flash storage is not a
hard drive...these are two different storage technology terms and are not interchangeable. So with your retina MacBook Pro...the term "hard drive" should never be used...UNLESS...you are talking about an external hard drive plugged into your computer.
According to Apple...the storage for your computer (flash storage) is not or was not meant to be upgraded by the owner...but in theory it is possible to do it...if appropriate upgrades can be purchased.
For your computer (which currently has 512gig of flash storage)...at the time of purchase/configuration...a 768gig flash storage device could have been installed (by Apple). This flash storage upgrade (at the time of purchase) would have cost an extra $1000 dollars...YIKES!!!
These flash storage upgrades I do not believe are easily available at this time (they may be in the future...and they eventually will most likely be less expensive). As a student...if you have to budget for beer...I'm thinking that spending $1000 (or more) to upgrade your retina-MacBook Pro's storage is out of the question!
You mentioned wanting to upgrade to 1 terabyte. I'm not even sure 1 terabyte internal flash storage upgrades for retina MacBook Pro's even exist at this time. But if they did/do...I would "guestimate"...that they would probably cost $1000+ (based on the current costs of 500gig and 768gig upgrades Apple offers)...which are $300 for the 512gig upgrade...and $700 for the 768gig upgrade (prices have come down from their original levels).
The "best" storage upgrade path for you at this time...is to continue what you are doing...which is using external "traditional" hard drives.
- Nick