Option 3 will break simple-netaid both the frontend and the backend.
Option 1 may not need any code changing.

What is the advantage if any of naming an interface eth0of1? Why eth0
is appended with an 'of1'? Why not just use eth0, eth1, ...., ethN
instead?

--
If you can't explain it simply, you don't understand it well enough.
(Albert Einstein)
If you cannot make abstructions about details you do not understand
the concepts underlying them.