First of all the shell you bought is not "better" than a jacket with insulation, because they're both designed differently and have different uses. It also comes down to personal preference.
The shell you have is great when the temperature is not super low and you're sweating more than freezing, an insulated jacket performs best when you mainly need it to keep you warm. Like you said, your shell is designed to block raw water droplets (rain) and let out heat vapors (sweat). The problem is, if you're gonna ride in really cold weather, you're gonna have to layer up beneath it. Layering up does not mean wearing 2 cotton tees under a hoodie, because unless those garments are specifically made to be layered, then all they will do is trap your body heat and eventually start to soak because they won't be able to evacuate the sweat that will form...making you potentially freeze.
So unfortunately, your purchases may not be over, as you will have to buy a first layer shirt (specifically designed to be worn as a base layer in winter activities) and possibly a second layer wool or fleece garment that is a bit thicker and will keep you warm all while still being able to breathe and ultimately let your jacket do it's job.
The powder skirt will work...somewhat. They sometimes can be attached to the matching pants that go with your jacket, but personally i don't find that setup very comfortable. Just tighten it (like the bottom of your jacket) and it should help once in a while when snow tries to shoot up your back/chest.