Yes, try combination synchroniozation. You can extend to N - systems

yes.it is possible. using chaotic masking technique we can increase the number of systems which leads the communication strength becomes increasing (multi layered masking). but practically we get more noise and error to confirm the theory.

Yes, but it becomes more difficult for implementation.

Yes. See, for example,

Chaos. 2008 Sep;18(3):037108. doi: 10.1063/1.2952450.

Synchronization in networks of chaotic systems with time-delay coupling.

Oguchi T1, Nijmeijer H, Yamamoto T.