I'm not happy with your installation plans. What looks good for a breadboard model, is not normally applicable in a larger area.
Inside a car (5m) 12V are used, for longer distances 24V. These higher voltages will reduce currents, and consequently power consumption and losses. Consider to use such voltages with a central power supply, and break the voltage down in every node of your home automation network. Don't forget fuses, or you risk failure of your entire installation on a local problem.
How do you intend to control the many relays? Individual lines to every relay will sum up into a huge number of wires. Better were a bus system with addressable nodes (I2C, CAN, Ethernet...), that also can be extended at any time. Line drivers are almost required, for secure signal transmission, so that I2C can not be used across a house.
I'd not try to build a cheap and unreliable home automation system, unless I want to make my living from service and repair.