There are one of 3 ways to do slin. The first way would be to do 1 to 2 iu with each meal you eat, 5 to 6 times a day. This will definately get you big as long as you are eating right, getting plenty of carbs along with your protien. This is the best way to get the most out of what you eat and also the least amount of risk of going into shock. You definately want to get a good amount of mixed carbs(lots of fruits and vegies, some dextrose in PW shakes,) with each meal, and around 40 to 50 grams of protien with each meal also.
The other way would be to do 1 to 2 iu slin immediately PWO with your shake, and I mean a shake that contains 40 grams of protien and at least the same amount in dextrose. You work your way up from there by 1 to 2 iu a workout until you hit 10 to 12 iu. I personally wouldnt go above 12iu, but then again, I am conservative when it comes to slin.
You can also do both methods at the same time, but I dont reccomend it unless you are a pro and know exactly what you are doing.
Slin wont diminsh the effects of GH. They would actually work well together as long as your not doing GH injects and slin injects at the same time.
I have personally used slin without GH and with the first method and was amazed at the gains in weight.
Slin and GH used together are very synergistic if used properly.