I'm trying it out for 30 days. So far this is what I've found. I'm syncing out of google into flock. My plan is to at some point delete all my contacts and calendars out of google. But we'll see. Yes it does allow syncing multiple accounts. And multiple calendars from the same account as well. Groups are not supported (yet as of v0.51) but hopefully this will change in the future.
Not sure about the answer for your other question.
Not sure about the answer for your other question.