I have created a requests section in the discussions, should anyone want a building covered by this mod. I will only handle buildings covered by the existing dependencies, or other buildings in my modpack.

The longhouse was overlooked in slopeless.

I have such a long modlist that it would be a bit prohibitive to copy each one from my steam workshop folder, rename, and enable them all in FCS. Is there a less-labor intensive way to set up the work environment in FCS?

As far as I can tell, though, this longhouse building may just have been an oversight in Slopeless.

"I cannot be sure that the problem I encountered is not in some way caused by my vast collection of mods"
That depends on which parameters you edited in order to fix the mod. In the editor you can see all the mods from the modlist that edit the same parameter. Congrats on solving the problem by yourself.