Task manager, posix compatible libc odds and ends, maybe another 50Kloc, Graphics driver: 10Kloc, window manager 2500 lines.
So not that bad, you could do it by yourself in about 2 years of hard work, probably less than that if you use a VM instead of actual hardware if you're a halfway competent programmer. I've done it.
Wow, Unix is a work of art. I have hobby projects at 2x SLoC which are literally just small web services :(