Arduino. Am I understanding the connection correctly?

Question

Arduino

I apologize for the hackneyed question, but life is more expensive and I want to ask the professionals if I understood everything correctly ...
I am another person who decided that he is a "genius" (actually not) and what a smart home can organize) Namely, light control in your own room.
I have read a lot on this topic and watched videos. and I want to implement this trace. way. I have:
- arduino nano
- double relay ( www.aliexpress.com/item/2-Channel-5V-Relay-Module-...
how I imagine it:
I pull the switch out of the wall and connect my bundle between it and the network : arduino + 2 relays.Why
2 relays?because I will control the lighting with one, and the second one is used to power the arduino itself.Did
I understand everything correctly?
Do I need other relays? after all, one should be on 5v (which I will control), and the second on 12v (which will power my arduino)
or how does it work?
Is it possible to use this converter to power the arduino (if so, which is better. relay or converter)?
www.aliexpress.com/item/AC-DC-5W-450mA-Switching-P...
it's just that there are an abundance of examples on the Internet and everyone does it differently, and somewhere one relay, somewhere two. where is one and the converter. and I'm confused...
will be grateful for the help!

Answer 1

The relay does not power, but acts as a circuit breaker. Hence the question - why do you need to turn on the arduino through the relay? maybe it’s easier to find a terminal block and plug your power supply into it so that it works all the time?
of course, it’s better for you to use the second option to power the arduino www.aliexpress.com/item/AC-DC-5W-450mA-Switching-P... , and already use the relay to control the light

Answer 2

answered here