> Can you just declare a static array and return a pointer pointing to any part of it? Like in the C example?

Indeed:

    lazy_static! {
      static ref BUF: [[u8;1024]; 16] = [
        [0;1024], [0;1024], [0;1024], [0;1024],
        [0;1024], [0;1024], [0;1024], [0;1024],
        [0;1024], [0;1024], [0;1024], [0;1024],
        [0;1024], [0;1024], [0;1024], [0;1024]];
      static ref BUF_INDEX: usize = 0;
    }

(You'll need to re-implement a `push_str` method on arrays yourself though)

> BUF is also visible to other parts of the program, correct? If so, it's not quite similar to the C example.

No, because it's not marked as `pub`, nobody outside the current module can access it.