Wow, 5 minutes and you already get a Guhong. That's intense.
You can either buy the Guhong II or the 55mm Zhanchi (which I heard was really awesome), though you'll want to save those cubes for once you reach 20 or 30 seconds, honestly.
Since you're not really at 1 minute yet, I'll just recommend that you learn fingertricks...simple as that. Of course, providing a video of your solve will help but for now I'd just work on fingertricks since they can carry you down to around 1 minute 30. :3
Also, you definitely have time to learn notation. You don't need to go memorizing stuff yet but this will help once you reach around 1 minute. http://www.youtube.com/watch?v=BP3V7Jhvt88
By the way, what method do you use?