btw, what is the "proper" way to handle something like this?
what i am doing now, is using quick select, refining the edges, creating a layer mask from that, and finepaint details on that mask.
afterwards, i create some adjustment layers and duplicate the mask there, if i want them only to affect those. and then i link them together and put them in a group.
only problem, when i find a mistake later, i have to reapply the masks on all adjustment layers by hand..
for the adjustment layers you can make a clipping mask
You can do this by hovering the mouse on the line between the two layers, hold down Alt or Option, and when you see the cursor change to a double circle with a tiny, left-pointing arrow, click.
Prior to and/or after making changes to a layer I always duplicate the layer, turn it off, and move to the bottom. I will also do this before I merge layers as well. I also use smart layers and smart masks so I can make changes to them later.
As for the image, for me, the background and foreground appear flat or without dimension. Follow vanishing point rules and remember that objects in the back ground get slightly blurry the further they are from the foreground. The third structure back is way too dark, it lighting doesn't match the other structures.
I agree with iamsam about the flatness. Slight blur and greying out of color makes things recede and adds dimension.
There is also too much color difference between the figures and the structures. I would add some warmth to the buildings that are closer to the front. You could add cooling to the figures, but it already has too stark an appearance if you ask me.
I think ....think....I'm confused. Seems too busy, I dont think it is the number of things here, its the difference in color / hue / contrast. The advice above about attaching adjustments is spot on. Let it rip, play some more and show it off!!