Level/World and objects, actors Scaling question

I’m not quite sure how to ask this but I’ll give it a try anyway.

I haven’t decided if I’ll be using Unreal or not. So far this is just a C++ project I’m working on

Let’s say I want to make a game that takes place on a planet, Mars, Earth, etc.

I want to make the Game world wrap back on itself in every direction so that When player leaves from point A in one direction continuously, they eventually wind up back at point A.

Now that’s another matter entirely.

What I want to know, is if I make my 3D models such as trees or rocks, buildings, and humanoids and perhaps animals or aliens (Who knows! lol) and I make those 3d Models to scale in something like Blender, so that the Human Male character is the proper average height of a human male in centimeters (cm) and the trees and animals and such. All modeled to scale of 1:1.

I think I would need to scale the Earth or Mars down as the game world, the memory requirements for a fully sized planet would be impossible to obtain?

I know there are other tricks to have the world split up into smaller levels that you can transition seamlessly so I will be using that to my advantage.

I’m just really stuck on how to implement scale…

The game will be Isometric Top Down. So I think that helps with rendering…

I also think I read somewhere that its better to make your models bigger to begin with because you can always scale down?

Any help with how to scale my game world and assets would be greatly appreciated. Sorry if what I wrote makes no sense ahead of time!