if every door is the same exact shape*, you only need to make one. you’ll need to paint different textures, and have different height maps for grooves, but you’re pretty much only going to need to make the number of doors as are different shapes. you can also scale doors to make them bigger or smaller. So, if every door is rectangular, you’ve only got to make one.
walls are much simpler, you really only need to make one wall for all flat walls. then you’ll need to make custom walls for curves, or for connecting diagonal pieces with straight pieces. But there are “brush settings” called “additive” and “subtractive” in which you can cut out a piece of another object, and then say for windows, insert the glass and window pane and decorations separately. So, 1 window, per shape, then use different textures. you likely wont even have to paint glass, you can just use drop in textures for most of them, then paint a few for some added spicy flavors to your 5 year old project.
i wish i would have known these things a year ago. I wouldn’t have wasted 6 months trying to build something that I could’ve done in half the time or less. ****… good luck if you plan on reviving the project.