Questions on level prototyping in unreal engine

Without going into too much detail to spare everybody some time here, I just have a couple of questions.

I am currently working with assets and theme, along with some environment.
When I gather everything I need, I want to start planning out a giant map for my game.
I want it to be very “metroid prime” like.
Just one giant world, with small corridors and arenas inside it.
The entire game is focused in the world and is mainly linear (with a lot of back travel) (even sort of like half-life 2 levels)

My general questions are:

  1. Is it possible to create an entire world map in the unreal engine?
  2. when it comes to load times and optimization, can you single out different portions of maps? (for instance, a lot of rooms in metroid prime are cleverly loaded behind a door before you can enter, with the load times being masked by the doors animation and a small wait time)
  3. Before adding in serious LOD and other designs into textures and meshes, can you prototype an entire map out and add notes at certain locations for artists and programmers to read?

My general idea is, before I start adding in programming and blueprints, I want to create an entire realm where the gameplay happens, (keep in mind its a singleplayer only game), Do you think this is possible?
Or is there a smarter way to go about doing things?

*also, scale, what would you reccomend I look at and read for scaling? I’ve messed around in many level editors, and I feel comfortable with level design in Unreal Engine.

I appreciate all feedback and ideas!

Yes, you can do this all with unreal.
You should read up on how UE4 handles level streaming. Level Streaming in Unreal Engine | Unreal Engine 5.3 Documentation
There is a bunch of tutorials on youtube that explain how to do it.
It is pretty easy to do
Level Streaming will handle the singling out different portions of your map behind walls and doors that you want to do

As far as prototyping the the whole map for size and scale I usually start with BSP brushes
because it is fast, and you can get the whole layout of your level up in a few hours with BSP.
and then you replace the brushes with real assets

for scale unreal units are in Centimeters. So that makes the whole thing really easy