How warm would the Beta AR and the Hyllus fleece goody fair in sub zero hiking weather?

This is a great system for cold weather activity because you can regulate your temp according to activity level and temp. For a proper layering system, start with a close fitting wicking shirt (like the Arc'teryx Phase AR) to keep sweat off your skin. The Hyllus would be the next layer (typically referred to as a mid-layer), then the Beta AR for the outer layer. For warmer temps or high activity the Hyllus can be your outerwear and will block most wind and snow, but breathe very well so you don't overheat. If it's extra cold, windy or wet, the Beta AR over top will keep you dry and comfortable, and for summer rainstorms can be worn over your baselayer to keep you dry and not too hot. The Beta rolls down quite small so it doesn't take up too much room in a pack. Super versatile kit.

Yes the centigrade scale,and would the Hyllus be considered a strong base layer?? I've only ever gotten down insulated coats. I'm new to the layer system.

I assume you are refering to the centigrade scale. Put on a nice baselayer underneath and you should be fine. If you are referring to Fahrenheit - damn thats cold! and you will most likely need a mid layer.

You should be pretty warm, although there are plenty of choices that'll serve you as well or better for a whole lot less money... Try combining the Stoic Welder Hi with a hardshell like the Patagonia M10 (which is on sale right now), and you'll save some weight and a couple hundred bucks.