Several have already pointed out that it's important to avoid blarges. In your case, you probably won't have many double-whistles on your OOB line (I hope not anyway).

When I went through my first "official" camp, a beginner's camp in 1997, we were taught on PCs to go straight to the PC call. On blocks, we were taught to stop the clock with the fist first and then go with the prelim. At the time, we were told the PC signal was also a stop-clock signal. Was this ever true?

Except in the corner, maybe :)

I try to slow down on block/charge calls, but I've noticed partners who call a charge with a point the other way. I let partner take those, natch.

Because it slows you down. If officials at all levels of high school just pointed, they might point the wrong way. That does not mean that you could not disagree with that, but I think at the high school level (and even the college level) we should use the stop clock signals. I guess on out of bounds call usually does not cause a problem, but it can. I have seen people using the stop clock signal not pay attention on point the wrong way while the other partner signals the other way.

Peace