Hi,
I also had to set up a PCI nic because of the operating system i was using did not support Wireshark. I had a lot of issues using the command line and manual XML because i am also new to a lot of the unraid but there is a really easy way to manage all the PCI stuff by using virt manager.
have a look at this post
Virt Manager is much more powerful to use than what unraid has in-built. Once you have set up virt manager, all you will need to do is go into your virtual machines hardware settings and add a new "PCI Host Device". just make sure you don't select your Eth0 device, since that will pass over what unraid uses for management. Vert manager will actually have a little "(eth0)" or "(eth1)" at the end of the device name in the pci hardware list to make this even easier.
If you want to switch what unraid uses as Eth0, take the array offline, then go "Settings > Network Settings > Interfaces Rules section"
you will see the network devices as MAC addresses. switch these around.
Lastly, if you have trouble seeing the device in your PCI hardware list you may need to check IOMMU setting in your motherboard bios