Best way to create a big city for multiplayer and what is handled by server

Hi, our current project is a multiplayer (up to 64 players) game taking place in a large city.(not as large as a GTA map but quite large)
As it’s a lowpoly style game, we don’t use terrain, all is made with fbx meshes that we have already made.
The camera is placed in a “topdown” position so there’s no sky and the view distance is short.
The game is planned to being run by dedicated servers.

Now our problem is: how should we setup the map to get best performance?
Should we make the whole city as one map with thousands actors or split the city into sectors, each sectors made in differents maps and use the level streaming to load/unload them on demand?
As it’s a multiplayer game, I’ve read that when one player enter a streaming volume, the map will be loaded for every player, is that true or will the map be loaded only for the player and by the server?
Is it better to have the server constantly loap/unload maps or having everything loaded on start?
Others options?

Well the best practice starting from scratch is to try and keep things into a more manageable bite size pieces on what would be expected of how much time resources is required to finish the project in hand.

Your typical Indy team usually requires the individuals of the team to pick up tasks based on a broad range of skills so someone working on an environment one day maybe doing the player animations the next so if you have ten devs working on a map then large world would be an option. If you have only one person responsible for the map assets you will land up having a real problem if for some reason they have to leave the project and if the project is large scale it becomes difficult to even try to pick up where they left off.

In a perfect world it would be nice to say load everything at once but the reality is an impossible question to answer as it is a bad idea to dump everything onto the sever and expect every thing to work out of the box and if your game does not have an established player game server crashing will more or less kill your game.

So short answer, kind of, is start small and scale up as UE4 makes it easy to build things as manageable components of the larger project and migrate them over later and then make decisions based on facts.

Optimising. Figure our how to do like the fallout3 form is. I know it is more to it than that but that analogy is a good one

I understand that 64 players will access alot more than one person at all times. The only way I know is to learn anout that side and how to stop use of processes that dnt need to be used like Notch has don in Minecraft. Goodluck

Thanks but my question was not about “how to work on making a big city map” or “how to manage a team to work on such project” but about UE4 and especialy level streaming and how UE4 network handle the level streaming thing.
The UE4 documentation is really poor about this when it comes to multiplayer and even more about multiplayer openworld