Hello, I have figured out how to weld together and import/export a wall/window prop into a solid piece, however I am lost as to how to get a single seamless texture to apply to the whole thing. Currently it still will apply itself whatever (single) section I have selected, and the other selections will not match seamlessly because it still shows the seams. Apparently I am missing a step in here somewhere. Suggestions? Thank you in advance.

If I get you correctly I have bad news. Your newly created prop won't work as you expect without being UV mapped. A procedural texture would do what you wish as it doesn't need UV mapping. the free UVmapper from Steve Cox or the UV mapping function in Blender will remap your new wall object easily so you can add the 2d texture map.