GRP decat seems to be the default choice here unless you had a specific reason for the Milltek one, such as if you wanted the Milltek exhaust as well and wanted to keep it all the same brand.
My take on the valve controller is that it's up to you. After break-in, you can drive in the sport mode, which opens up the valve and you get *most* of the sound that you'd get with the controller. The controller makes it fully open and you get the most sound, but I am not sure if it's a big enough difference. So, IMO, the only "benefit" of the controller is being able to fully open the valves in touring mode. I don't know if that's enough of a reason to get it. I know that for me, when I am driving out or coming home, I don't want to bother my neighbors so I like it to be as quiet as possible.