The only thing you MUST do despite everything you’ve already been doing for archviz in 3DS is to assign a new non-overlapping mapping in the second map channel of each one of your objects.
So lets say that you have a table and it has a UVW map that you have already applied to adjust its materials. Then after that you apply the Unwrap UVW and make sure to set the “Map Channel” to “2” (you can see that at the very end of the printscreen you’ve just posted. Then you click “Open UV Editor”, select all the faces and spread it by face angles (or anything you like, but you must be sure there won’t be any overlapping faces). Unreal needs that second channel to apply the light results of its calculation to every object in your scene after you build lights using lightmaps. There are tricks and tips to improve that mapping, its a critical stuff to get nice lighting in your scene. You should read this to get a better idea: Understanding Lightmapping in Unreal Engine | Unreal Engine 5.3 Documentation
One tip: every time you read anyone talking about something in Unreal that you don’t know yet, look for it at UE4 documentation. You’ll end up learning a lot of nice and important stuff (that people will probably bypass in a forum answer or archviz straight forward tutorial) that will save you a lot of hard time struggling to get nice results in the future. 
