cortana + raspberry +8 channel relay

Are you planning on running Cortana on the Raspberry Pi itself or are you planning on running Cortana on a mobile device and then connecting to the Raspberry Pi to control the 8 relays ?

If you are planning on using Windows 10 IoT core on the Raspberry Pi then there is a step-by-step guide for getting started with Cortana on IoT Core here which may be of interest:

https://docs.microsoft.com/en-us/windows/iot-core/extend-your-app/cortanaoniotcore

There was a project on Hackster.io using Cortana on a Raspberry Pi running IoT core to control some motorised blinds, which may also be of interest:

https://www.hackster.io/cyborg-gibson-11/automated-blinds-by-cortana-7bfaff