As far as I can tell, there's no such thing as a USB PVR350. It's PCI only. The PVR USB2 is hardware encode only.

I'm not sure how good the linux drivers are for the USB tuners either so that's something to look out for.

Are you saving the one PCI slot for something else?

You also might find some difficulties getting the TV-out on the mini-ITX board working correctly (overscan in particular). Generally speaking nVidia cards are the easiest to get going I think.