Finalization of Concept:- I have define requirement as below.

1. Making Smart Switch having 5 Switch & Can controlled by WIFI.

2. It Can operate withot WIFI by physical Switches or Pushbutton.

3 Switch can be DIY mode so it can be RE-Flashed.

4. It can fit in existing switch board without changing any switches or wiring.

5. ALL GPIO of Microcontroller to be used as it is DIY mode.

6. Switching device should SSR & zero crossing to avoide noice & switching surges.

7. Size of PCB Should be small enough so it can fit in existing switchboard.

As we finalized requirement , next step is to select hardware.