Yes. Technically you can have a cantelever with 51% of the material supported and 49% hanging out in space (you just won't be able to put much load on the cantelevered part and it won't be particularly stable).

Falling Water is incredible - and yes there are issues with the concrete mix being incorrect, as well as the reinforcing. There are a lot of cracks and such due to shifting, settling, etc. but it still stands after all these years - beautiful as ever.

That skywalk looks hella cool. I'd love to check that out!

I did house painting in Oak Park one summer. Interesting area. Pretty ghetto, but the houses near the Frank Lloyd Wright houses are well kept and expensive.