Yeah, if you're going to keep watching, definitely avoid looking things up "out of curiosity" because you'll open yourself up to all kinds of spoilers.
As for the bystanders, I think they touch on it a bit later, but even though 80% of the population is born with some sort of quirk/power, not all of it is useful enough to save people with. It's why people still work office and retail jobs. They have power, but it's too weak.
two things to add to this:
people generally aren't allowed to use their quirks unless they're heroes
it hasn't been explicitly confirmed in the manga (yet), but there's reason to believe that the quirks in Japan's general population might be weaker than those in other countries