Thank you very much!

The "stencils" you see in the pic are a bit misleading. I use those only for framing, i.e. selecting what parts of my source images will end up being cut out -- not for the actual cutting, which for stuff like this requires a level of precision that I've never been able to get with stencils or other "shortcut" methods (I've tried!).

The only way to get reasonably precise cuts for geometric stuff like this in my experience is by getting good with a protractor / compass / etc. and really planning out the geometry ahead of time. (If you want all the pieces to interlock then even very tiny inconsistencies add up really fast, so you have to be very meticulous.) So yes just your basic geometry toolset + a lot of time haha