EMPIREBUILDERDAVE,
I go out of my way to avoid any warpage on my structures. On a building of this type I would have applied some bracing strips (say 1/8-inch square basswood) to the inside corners of the walls, around the insides of the window openings, and possibly elsewhere. I might also have added doublers (1/16-inch thick basswood sheet) to the insides of the front and rear walls extending all the way to the tops. (That could still be done on your model even at this stage if you think it's worthwhile.) I would then have assembled the walls and stained/painted them inside and out after the walls were assembled. Yes, there is a large front window so you want to be careful to have a realistic look on the interior bracing. My technique is certainly not the only way to do it, so this is just a comment, not a critique, and I hope you find it useful. And I don't think you will have a problem with this building. Please keep taking photographs during the construction process. I'm interested to see how you go about it, as well as the finished product. Who manufactured the kit?
Picture below shows a similar building that I completed in 2018 from a Bar Mills kit. It was difficult to preserve alignment and minimize warpage at the front due to lots of "glass" in the fragile front walls. And if you look carefully, you can see some warpage at the rear of the newsstand.
MELGAR
