Correct networking design

Hello guys, i have just started to learn how to use networking in UE4 C++, i have started with this tutorial: UE4 C++ Network Multiplayer Game - 0 - YouTube

My game has singleplayer & multiplayer modes, each of them using the same classes, so it should be the same logic only on the singleplayer, all the network code should be ignored
I am wondering in a big game scale, what is the correct design regarding to the networking’s code implementation & the actual logic’s code implementation
Do you think that both of them need to be in the same class? Or it should be separated? If so, how will be the design?

That is a good question since MMOs have to be handled differently, but Unreal’s built in replication relies on the structure of Actors and their Owning connections.