How to exactly setup the landscapes for underworld sea

Development World Creation
1

Hello,

I want to create a underwater sea living organism world.

My target is to have:

  1. The bottom floor at starting z = 0
  2. The main floor starting above the bottom floor while making the bottom floor “invisible” to see
  3. The overworld area with mountains or islands etc.

The bottom floor will be used for “caves” so player can swim down into it.

I am new to unreal engine and just played around in cinema 4D with little little small stuff.

But from what I watched yt videos I need 3 landscapes right? How much would 3 landscapes alter the usage of cpu/gpu? Or is there another way to keep it more ressource safe?

Thanks!