No max file size limit.
We have CDNs around the world to help with network speeds. Of course, that's a vague answer for now, but we're gathering more data on upload/download speeds as we let more users in and will have more information on this in the near future.
Definitely not planning on firing anyone for using too much. The only case we'd ask someone to stop using our service would be if they're abusing our policies (i.e. 100 people on one account). So far we've been fine with an "expected value" type system -- some people will store/stream a lot, and some won't, but overall it all works out so that the $20/month price point works out just fine.