At the 14U level and up it's more dependent on the catcher's throwing ability and the speed of your runner. Sometimes at that level you need to do the unexpected to succeed.
The only time I use a TRUE delay steal is late in a game when I need a run or a base runner is scoring position. Otherwise all you do is wake the opposing pitcher and catcher up. Let them keep napping all game long and then use it when you REALLY need it. I have found there are very few kid who really understand how to delay steal and the timing of it.
I'll hit and run on any count. Again, it depends on your hitter. IF she has good enough bat control to hit to the right side or put the ball on the ground I'll do it. If the hitter is spotty I'm not so inclined to use it.