The idea is awesome as always. I'd try to be careful with so much photoshopped images all together, it's good for concept art but not for a photorealistic result (if that's what you want to achieve). I'll write what I would try but before that I want you to know that I probably wouldn't be able to do half the things you do <img src="e.deviantart.net/emoticons/s/s…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="391" title=" (Smile)"/>
The sky lens looks different by the rest, in fact the town on the island looks a bit too"isometric" compared to the rest. there's a bloom of light in the middle-right of the terrain, that would hardly happen because the atmosphere at this distance wouldn't be so strong, the density of the air particles is not that strong. It seems like there's a lot of dodge/burn on the houses, probably the light didn't match and you had to adjust it, but consider that light doesn't work the same way on all materials, and especially dodge gives a plastic effect, it's missing roughness.
Now these are all technical issues, mainly they can be solved by using 3D instead of photographs, or even 3D mixed with your own photo projections.
I totally love your ideas and if you manage to achieve total realism they'd kick asses even more, so I try to help with the few knowledges I have <img src="e.deviantart.net/emoticons/b/b…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="366" title=" (Big Grin)"/> Thank you for sharing these extremely cool images by the way, you really inspire me each time you post a new work!
I bought a subscription to the the gnomon workshop, they have some videos of syd mead that blow your mind,there are also in-deep lessons about anatomy, perspective etc...I taught I knew almost everything about that stuff, then I saw the videos and...I felt like John Snow man,I know nothing