Hi GeeksGoneBad,
Using modularity in your levels would probably be the best route to take. If you were to look at any of the examples from the Marketplace you would see that all of the levels are built using many pieces of the same geometry, especially when dealing with walls or flooring. Things like this are best served using modularity.
Using modularity will also help you stay sane when it comes to creating a UV for your textures and for your second UV channel for lightmapping will be able to have decent shadows without having a huge lightmap texture.
There are some good tutorials and insight provided by Hourences site and WorldofLevelDesign.com.
Some information about lightmaps provided from our documentation can be found here.
If you have any other questions feel free to ask!
Thank you!
Tim