Hey there @RadMcCool! Welcome back to the community! Everyone’s pipeline is a bit different, and it’s best to go with a pipeline that suits your style best!
How I work is making all of the pieces separately and then arranging them in engine, as you can handle modularity much easier instead of having to reimport assets constantly. This is especially useful if you are going to be placing groups of assets procedurally. This way if you need to only have say the front wall of a modular building, you don’t need the whole thing. This is common practice in multiple of the studio’s I’ve worked in.