The article is quite sound and doing all this is standard practice in the embedded world where you can't afford the size of glibc. The article is a bit incomplete, but presumably he'll address the rest in his next installment.
As a preview, to provide the correct C ABI to main() you need to zero the BSS (this is how your static variables get initialized), maybe copy the initalized data, call the constructors and destructors for C++ / C (gcc extension), provide memcpy() and others stdlib functions (which gcc will use even if you don't), etc. You can do all of this without assembly in C, but it does take some effort.
As a preview, to provide the correct C ABI to main() you need to zero the BSS (this is how your static variables get initialized), maybe copy the initalized data, call the constructors and destructors for C++ / C (gcc extension), provide memcpy() and others stdlib functions (which gcc will use even if you don't), etc. You can do all of this without assembly in C, but it does take some effort.