Pharo is bootstrapped, and its building process starts with a really minimal image (even the compiler is not included). It is possible to build custom images of any size. You need to take care of packages and dependencies, of course.

Pharo can make applications with a native look & feel - https://github.com/pharo-spec/Spec-Gtk.

Current Pharo has a very solid and powerful FFI, so using C libraries is easy.