Re: causing no (serious) harm
That's a good few years' worth of questions right there, so I'll just pick up on a couple of points:
'Aiki' can be difficult to translate, and like 'harmony' can mean a wide range of things. As the name and a principle of a martial art, it was intended to mean something more than just commonplace 'blending'. Its almost deliberately vague, though. The point of it being an untranslatable term is just that - there isn't an exact translation.
I once asked a Japanese friend what it meant. After a bit of though, she said that when she and her brother were fighting as children, their grandmother would say and tell them they needed more aiki.
That'll do for me - harmony, understanding, compassion and an ability to come to a mutual understanding. Its a physical and philisophical principle. As far as O'sensei mean to use it, although I never asked him, since he refers to Aikido as a Way to Heal the World, I doubt he meant a Way to Heal the World by Breaking Wrists Easily.
In general, aikido should provide a way to do any amount of damage to an attacker - from lethal damage to no damage at all using the same technique. Kotegeishi can kill, if you flip someone on their head onto concrete, and it can certainly take someone to the ground without causing any damage at all. Shihonage and iriminage are also good examples.
Its personally one of my favourite things about aikido - that you don't have to damage an attacker. If attacked by, say, an autistic teenager, how would a Tae Kwon Do or Arnis practicioner handle it? I'd suggest the result would be much better (especially for the person you really don't want to hurt) using aikido.