I am looking into getting this as a way to get around having to learn 3D camera systems (which seem to be just slightly beyond my ability to figure out) but if I am to go all in on Fauxton 3D I need the ability to have backface culling so I can do indoor environments without having the view blocked by the walls when I rotate.

It doesn't have it built in, but you can add it using the "gpu_set_cullmode()" function that Game Maker has. Please keep in mind, however, that this system is for sprite stacking, and doesn't have .obj model support built in, so back-face culling won't be incredibly useful for sprite stacks since they are essentially a stack of 2d planes. This is mostly a quick and dirty 3D solution for beginners, but it should really only be a stepping stone to learning full 3D IMO. :)

If you want to learn more about 3D in Game Maker I cannot recommend Dragonitespam's 3D tutorials enough! They are really well done, and pretty much how I learned to even make this system! haha. 

Best of luck! :)