1. You can always see those areas in UV editor or save the UV's to Photoshop where you can mark those areas with guidelines or so. There are also tools over the web that helps you deal better with UV's allowing you to shift, scale, rotate the UV's however you like. The tutorial's archive now contains the scene and the textures and you can better see what I mean.
2. Yes there are overlapping UV's but this asset was not done for baking AO or something else having so many tiles and overlapping areas. However you can create bake textures from overlapping UV's but is very tricky and depends from case to case, often it only works with symmetrical geometry. Though it can't be a problem for normal maps as they are generated from height maps based on the diffuse maps, so they also tileable, as well as the specular textures. Here it was not used a second UV channel, but some developers or engines are using this technique also.We did for some projects.
3. You have wright but depends from case to case. There are also a lot more elements to consider to obtain a successful asset like, obvious tiling, butterfly effect, repetition, etc. Also it depends on how much detail you have in that texture so it might not be a problem if you mirror it. In this case that window texture was used for five windows across the model and the texture space wasn't a real problem here. Maybe in what you are doing you can't see those buildings from close, in this case it might not be a problem mirroring it.
4. Again it depends from one developer, engine, level editor, console to another what technique it is applied. In this case the purpose was to show how much you can optimize one asset, this asset. Every developer must make tests to see which technique is best for their engine. As the latest engines and consoles supports more and more geometry budget it might be wise to use geometry (like you said), especially if this asset will be duplicated few times across the level, but like I said, being an example of one house and how you can optimize only one house this wasn't a problem.
If you have more questions or I didn't answer these feel free to ask. Also like I said earlier the tutorial's archive now contains the scene and the textures so you can better see the mapping, tiling, etc. You can find it on our website under the Share section
AMC Studio - game and (3d) graphics creation studio All the finest, Daniel