First of all, it is a very well put together set and I particularly like the different sizing of the shots. I think you were right with your choice of the main image, as the red of the funnels and warmth of the wood panneling really lift the grey mood of the sky.
I think there are options available that might improve the overall effect, but these are very personal things that may not appeal to you. I'd be tempted to crop out the BBC(?) building with the satellite dishes on the right of the main photo, but keep in the line of bollards as they work well. The light on the Maid at centre bottom makes the Waverley on her right look dull and dowdy, and I'm wondering if it would improve the feel to just tweak the levels slightly to bring them closer?
No need to say much more as basically it's a fine idea and well executed.