Like the Nike commercials say, Just Do it. I mean really, commit to doing it, and then do the following as a minium. 1. you need to learn to hurdle. Write me and I will help you with that. 2. You need to prepare some for the 400 and 1500. Give yourself 6 weeks for this. Run 3 300 twice per week, walk what you run. Run Three days per week, 3 miles, busting your arse the last 1.5 miles. If you have never pole vaulted, get someone to show you how to stiff pole correctly.
As far as potential, you are much better than I was at your age, you are exactly the same size I was and I was running the 400 in only 56, 100 in 11.6 I was a good pole vaulter going 14 feet., and high jumping 6'2 on average, with one 6'4" mark. The field events don't mean squat for where you are right now. You have all the time in the world to learn them. In the short term, you as good or better than I was and two years later I had won the U.S. Junior championships 7,210 with college implements and hurdles, about 7800 with the new lower hurdles and lighter implements they use today. (why did they ever lower those anyway...totally screwed up the record keeping)
So YES, you have more than enough justification to do a decathlon., just be fit enough to not blow the 1500 and 400. Also, the distance is necessary just not to fade on day two. And, if you run a 4:15-4:20 1500 like I used to, it will not matter if you stink in an event or two. http://www.youreonathletic.com