In general it'll be a judgment call. I think you could ask 1. and then ask 2. and 3. together. But 1. was already discussed either here or on MO, and I think 2. was as well (depending on exactly what you mean by "high school") although unfortunately I couldn't tell you what keywords to look for.
As for your last question, that's roughly what PlanetMO is for, and you might also want to try your luck with quora, although I don't know much about it.