2) I could but I would go broke in minutes. 99/100 people would reach into their pockets or purses and pull out a ring full of keys and would intuitively understand that their computer uses an application to do similar. If your faith in people is so low you think they're all morons, why bother encrypting what they have to say. They're idiots anyways, not like they have enough mental capacity to plan anything according to you.
3) By default it uses either pgp.net or MIT's hkp servers, I can't recall. Most public keyservers sync their directories multiple times a day. You can search by name or email: http://imgur.com/a/SSHlP
4) How does using gmail prevent you from using the built in Mail.app or have anything to do with the headers not including gmail stuff? OSX provides a system-wide onboarding process for linking your gmail to all the system apps...
5) So you can send user generated input that doesn't match what they wanted to send. How is that helpful?