I popped your model into both Meshmixer and into Lychee Slicer, both of which have hollowing features. The results from both were nearly the same, an inner shell of 2.5 mm (arbitrary choice) with an interior that has a minecraft flavor to it. I lack the skills to smooth out the zagged inside as well as those necessary to perform the window cuts. Consider to visit Reddit for 3d modelers with the requisite skill. Expect to be asked how much you're willing to pay, however.

https://www.reddit.com/r/3Drequests/