Can I use custom C code to interop with k/n (need to interop with the direct C libs such as treads.h, time.h ect....) Will it work?

You could write a C library to wrap the native functionality and then expose a simplified C API to interop with K/N. Or you can interop with the native libraries directly. You will need to use the

interop

either way to autogenerate the binding code.

Yes, and many standard libs already available as platform libs

where can i get them, cant produce them by myself for some reason (is there a repository somewhere for klibs of C stds?)