Will Google Buzz be merged or integrated with Google+?
I'm not involved in this directly, but here's the official response currently: Google+ won’t have any major impact on Buzz right now. Buzz users will still see a Buzz tab on their Google profile, and Buzz will continue working as it always has. Google+ users can also be Buzz users or can decide to just share their content using one of the products. Over time, we’ll determine what makes the most sense in terms of integrating the products.
Are their core groups of non-Google users you test early iterations on?
Not really, beyond bringing in non-Googlers to our usability lab to get early feedback on mock-ups/prototypes/etc. We mainly "dogfood" it internally with Googlers, but clearly with social products it's really important to use them in "the real world", so it's great to finally be in a public Field Trial, and we're learning and iterating in the open every day now.
Will Google+ integrate sharing posts externally via Twitter, Facebook, LinkedIn, etc.
We do currently support this in YouTube, and many users do find it useful for reaching their audiences on other sites about their YouTube activity. I'm not sure if/when we'll do this in an automated way on Google+, but in the meantime, every post you make has a permalink (click on the timestamp next to your post) that you can share on external sites (and many people do).
Are updates release all the time, or do you roll out a once a week batch?
We try to do a full push (almost) every day, and we sometimes sneak in patch releases too if needed. But there are humans in the loop, it's not a "auto-push if all tests pass" situation or anything like that.