CO-OP Server Architecture Question

Hello, I have a question about multiplayer architecture. I want to make a singleplayer/coop first person shooter. I have previous experience with programming multiplayer games with dedicated servers, but I am confused as to how to setup the coop game in Godot, and would like input, thank you. I am planning on using steam networking. Here are my current ideas:

  1. I can always have a local server running even when playing singleplayer. This is way easier for multiplayer, but will be alot of extra work, as the game will be split across two projects. However, would this require the player to open up both executables in order to play the game?

  2. Server and client in one, and use the scene tree to manage server/client. I am unsure of how reliable this is though.

Thank you.