Create Landscapes and Terrain Faster

I am a new developer creating an island game with a couple of people. The island has different sections. The player has to do something to unlock the next area of the island. So my question is: Do I need to create each section of the island separately? Because I thought I could just create one terrain island with unlockable barriers between each section and open those barriers by even triggers. Note: I am creating the island assets and most of the models in 3Dmax.

 

Hi! I sent a bug report but I'm not sure it will get through. After sending, Bug Reporter reports a connection error.

Contents Of Bug Report:
When I installed the Terrain and ProGrids asset. I tried to change the size of the texture brush using the hotkey - "[","]". Then I got an error with a hotkey conflict. I chose which option to use and clicked "Rebind Selected". After that, the problem was not resolved and I got another one - if I click on the left mouse button, my brush size changes. Drawing has stopped working. I can't solve the problem. Saves only "Reset Packages to Defaults"

 

When ever I try to use Height Map (From World Machine) I get This Result, is there anyway to fix