Finally completed the soft-latching power control part in the circuit.

2 Arduino nano(s) were k1lled during the process :*(.
Used an N channel MOSFET at first in order to control power going to the Arduino, failed at it, switched to a relay (big mistake), driven by a transistor, finally got out, bought a P channel MOSFET, still driven by an NPN transistor, and in the end, it works flawlessly, gave me immense happiness watching it work flawlessly :D