Upload & Sell: On
This looks great, but did and do you have written permission to use his image? I also don't think that it will fetch much of anything since it is not your original work. JMO.
As the one of the original photographers to recognize the sales potential of the Dallas skyline in the late 70's, I can tell you that individually they don't sell for a lot, but I've never sold one for less than 100 buck profit and I've sold hundreds and hundreds of them over the years, plus stock sales, billboards, and nightly news backdrops. If I had to guess, the great majority of those buyers didn't give a hoot about where the components came from. It's not like a Dallas skyline, no matter how good it is, is going to turn into an iconic appreciating artwork. If it's a good composition, and people like it, they'll buy it, frame it and hang it, and if it's really good, a percentage of the people who pass through through the office/boardroom, wherever, will ask where they got it, and want a copy for themselves. There's always a market for a cool image of a vibrant city.
This is all a moot point because you created it for yourself, it's unique in composition, and collaboration. You mentioned at the outset that you obtained permission to utilize the sky, the right and honorable course of action. Enjoy your creation, other folks will too.