For the "100 contacts" question, I'd think that would be any form of talking to somebody you don't already know. So, leaving a comment on someone else's video, tweeting at somebody, talking to a random stranger you just met in person about YouTube, etc. You can expand the definition to fit whatever it is that you want it to include. It's all driven by you, anyways. 100 would be a lot to shoot for, though. I think by that point, you'd lose quality in your interactions.
I noticed your little "I thought you might be interested in..." messages you crafted. Nix those. They're going to end up in peoples' spam boxes because YouTube hates when you send the same/similar messages to a lot of people. Just find someone's funny comment and respond to them in a funny way. That's how you do this.