HGH is a wonderfull drug but it is not for everybody. At this point, I would say the use of HGH would be unnecessary. You are still very young and can achieve so much more naturally. Afterall, at your age you would need quite a bit of HGH for muscle gains, certainly at least 5 - 6IU p/day I would say. Anything below that will mostly deliver fat.
If you go ahead and use HGH I suggest you begin with about 2 - 3IU p/day, and take it upon waking up. From then on you can start increasing the dose by how you feel. I would usually increase the dose by 1IU every 1 - 2 weeks (depending on how I feel) till I reach a dose that's doing the trick. Once I reach that dose I'll stay on that dose till the end of cycle.
Depending on what you want to achieve depends on how long you should cycle HGH for. Fat loss will usually arrive a lot sooner than muscle gains, so you can get away with doing a 4 month cycle as within that time you should defenitely notice some of that flab gone (providing diet/training/rest is in tact of course). On the other hand, muscle gains take a really long time to arrive especially if you are using HGH alone. If you are after muscle gains I suggest you use HGH for no less than 6 - 7 months and I also suggest you add AAS to your HGH cycle as that will make a world of difference when it comes to muscle mass. HGH + AAS is certainly a great combination if you are after gaining a bit of muscle.
HGH unmixed can survive up to 2 years providing it is kept at the right temperature, but once mixed you need to store it in the fridge and use it asap.
Take a look at this thread as it has a lot of useful information including mixing instructions: http://forums.steroid.com/showthread.php?t=265314
Moving on...
As I said above, if you are after muscle mass I suggest you defenitely add a type of testosterone compound to your HGH cycle. Sustanon 250 is fine, about 500mg p/week should be enough for some nice muscle gains. Keep in mind that Sustanon works best when taken ED or EOD. I guess you could probably get away with taking it every third day. You might want to give your cycle a kick start by taking some orals at the beginning of your cycle till the Sustanon kicks in. That's optional of course.
When stacking HGH and AAS, use HGH on its own for about 8 - 12 weeks before introducing AAS. You can certainly start HGH and AAS at the same time however it would be nice to give your body a taste of AAS while IGF levels are elevated.
HGH dosing times as follows:
* Upon waking up,
* Early afternoon
* Pre workout
* PWO
NOTE: (At your age you do not want to take HGH before bed time)
Once you breach the 3IU mark I would start splitting the dose into 2 shots per day.
You may want to stay away from consuming too many carbohydrates around injection time otherwise you may end up with some surprising blood glucose numbers.
This forum has a lot of information on HGH so help yourself by using the search function.
All the best.
-Gear