home automation with arduino, raspberry using externally powered relay board
I see a distance limitation problem.  USB appears to be the link between the controller and peripherals.  That puts about a 5 meter limit on how far away you can place peripherals.  There are workarounds to extend USB (search for "usb extender").  But most use longer distance protocols such as C-BUS or RS-485.

In this thread someone posts the link to the people who designed and published C-BUS.

In this thread people are talking about connecting a Raspberry Pi to Arduinos using RS-485 and something called the Modbus library.