1. The New Topic button will be at the very top of the Forums index in BuddyBoss 2.0. The new topic creation opens just below the forum, like in the new bp-default.
2. The activity comment box will be closed and then open up ajax style when clicked in BuddyBoss 2.0.
3. We are not adding a Twitter style homepage in this release. Maybe something for a future release. The code for the login box is in sidebar-home-left.php, so you could grab that code and put it into a custom front-page.php file on your own to do something like this.