PC and PS4 players will all share a single universe.
If you buy the game now then you can use the same account across both PC and PS4.
If you create a world then it will be accessible on both PC and PS4.
The perk is about helping craft and contribute to the main universe of the game for all players. Maybe you want something special that we’ve not thought of? I’m pretty sure @nevir will create something really unique. Likewise, when the time comes if you prefer to give us a creative brief then we can help you with some of the more technical stuff.