If you are only using gh by itself, I would not expect much gains in muscle. You may gains a little and you will get leaner, but without AAS, it will dot be very helpful for your goals. If you were to run it with test, that would be a whole other story. The synergy between the two will allow you to slowly add good, lean tissue. 100 days, about 3 months, is the bare minimum that I would run it. If you can get it started and and in 5 or 6 wks, order more, then being able to extend your run to 6 months, you will continue to improve over the entire period. 

As for using a slin pin, yep, it's no problem. You'll want to inject into an area with low amounts of body fat, like the tricep or delt. I always go IM with my GH. 

There are many ways that people have come up with for running GH. Personally, I like to split it up through the day and have found my results to be best that way. with 5 IU, I'd take 1/2 my dose in the AM when waking and then the rest about 6 hrs later. If you can get your hands on some IGF-LR3, take about 25mcg right after you're done training.