1.5" inch depth is pretty much the standard for glute injections, but I think that most people in this community would probably be fine with 1" needles as long as it isn't so shallow that it causes pain in sitting. There has been a lot of recent debate and research in the medical community about whether standard injections depths are sufficient in obese patients, but again, that probably isn't a concern to anyone reading this board. Even if you were to miss the muscle or to go shallow enough to have some leak out of the muscle, it shouldn't be a problem. Steroid hormones are lipid soluble and pharmacodynamics of anything but the shortest esters (or things like TNE) shouldn't be significantly different. Some people here are already doing their injections SC instead of IM, and some doctors supervising HRT therapy are telling patients that SC is fine to do.
As far as hitting the sciatic nerve, that shouldn't be an issue as long as you're injecting into the proper location (the upper, outer quadrant of each glute) and going in at 90 degrees to the skin surface. Please don't try to shoot into any other portion of the glute - if you were to do so, there are several nerves (including the sciatic) that you could hit and damage.