I already added a fuse (not mounted on the picture) in the schematic. For the varistore I saw it from other project but did not integrate it yet in my project but thanks for the comments for improvements :).
What would be the advantage of using an optocoupler to drive the relay? Note that in the video I posted, I'm not using the power supply (HLK-PM01) yet. Power is coming from the 5v of the FT232RL. Yet I'm having issue when driving a 220V AC light bulb.
Where can see see the eagle file of your PCB design?
@aze No Problem 
all the time nice to hear idea from people 
@Aze I don't think so your project can work the same way as this one. When seeing your PCB and connection schematics, I think that the uController needs to be active so that the switch can function. In this project, even though the uController is dead or hanging, the manual switch can still activate the lamp.
@jeremushka Nice to see that you could find the way to work with this project Though it looks very similar in the way I'm using my design, I'm wondering how you can connect the No and NC cables in between the smart switch and the physical switch. Since you mention that now the smart switch is inside your electrical box, does that mean that you have 2 wires traveling in between your electrical box and your switch box? I actually never though of putting a smart switch in my electrical box and I would like to know what I would need to have the smart switch installed inside the electrical box directly. In that case, the space constrain is much less.
@jeremushka I connected the ACS712 in series just at the output of the switching system. I updated the schematics for the connection. Note that in the code I have delivered for reading the ACS712 might not work out of the box for you. I couldn't really make good code on that because of the instability of my previous design.
@jeremushka I have uploaded an image where it is explained how to connect the smart switch with the 3 way switch but I think you got the idea right.
I've updated a new version of my design containing the comments and feedback I've received. Thanks a lot! I didn't try this design yet as I need to receive components from China. So it'll take around a month before I can test it. Anyway, I release my design already on this platform to get already some comments and feedback.
@jeremushka No, it is not connected to the arduino input. The relay is doing a 2 way switch configuration with the physical switch. As such, even though my PCB would be dead, I'm still able to control my lamp manually.
@gohan: I can fit also a ACS712 in the switch box. There is are jumper wires connecting to it. Based on the hall effect, I can tell when the light is on or off.
@Nca78 Thanks for your remark. I can't use an SSR g3mb-202p because I need to have a 2 way switch for connecting to my physical switch. I couldn't find smaller device. I'll give a try already with using the AU version of the Atmega.
Do you have any recommendation regarding the minimum size of my 5V traces?