Peak is slightly higher and duration slightly shorter when administered IM, and the opposite for subcutaneously, so when I was running GH, I would take those factors into account depending on what I wanted the GH to do at the time. Post workout, IM. Before bed, sub-c. Only downside to hitting the GH IM is a more pronounced feeling of lethargy and sleepiness. Some people I know have serious trouble with staying awake on GH, especially IM, but for me it was just more annoying than anything and fairly easy to overcome.
If you are fairly lean, then yes, 1/2 inch slin pin is fine for delts, bis, tris, pecs, even quads. Just stick it deep and plunge away (that's what she said).