Ahh. The answer to both questions is "PBTA systems are more player-driven than most systems." The consequences to most moves build their own drama, ideally, so the GM's main job is to set the tone, present situations, roll with the consequences of players' moves, and fill out the world with new stuff.
You might want to talk with potential players about what they want out of a game--if they want detailed singler-player exploration of their Lands, great! You can plan out some interesting locales. Play-by-post might be better for keeping that manageable/engaging.
But if they want the Homestuck experience--haphazard exploration regularly interrupted by shenanigans, game-breaking exploits, and text- or voice-chat conversations--then that's going to be a much more free-wheeling game. In that scenario I'd recruit my players to come up with ideas about the session, or even try the round-robin GMing approach so that everyone get to contribute equally.