There will be 3 kinds of worlds:
Quote from a developer
There is no official confirmation on this (at least afaik) but I´d assume that public- & private- official worlds will have the same properties in regards of size and gameplay elements.
You´ll be able to create your world within the limitations of the world builder tool. So while you are able to define a lot of details on your worlds you´ll probably not be able to pre-generate detailed structures. Those will have to be build ingame by you once the game launches
Here is a nice thread that shows some of the capabilities of the worlds builder tool.
Here again are some quotes from a developer on this topic:
So your world will definitely be playable by PS4 & PC users.
I´m not sure how to interpret those quotes in relation to the other perks though.
The developers mentioned that they want to hit 1.0 late 2016, but this was stated a while ago so this information might be outdated by now.
The Master backing tier seems to allow you to do that.
Though there hasn´t been much information about the details of the Master backing tier so you should probably bug a developer like @james with a PM here in the forum if you want additional information on this.
I hope this answers most of your questions.