To get mayor you need 85k and to apply on the forums. The posts are the 4 corners of where you would like your new town to be. For example post one would be: x= 100 y=64 z=100 and so on and so forth

 

The main world

 

You can go to any space that is open, and pick out a 200x200 area and mark the posts there

 

Anywhere you would like. You can ask in trade chat for someone to fly you to an open space above water or on ground, and just set the posts there

 

Moved to Help & Support.

 

You put your posts in the Wild, not the Mining World. You do /getpos in-game and it will give you your coordinates to post on the application.