I would get, in no particular order, wool socks, a pair of shin length knickers (Shebeest makes a nice pair), a windproof jacket or vest, full fingered gloves, toe covers, a headband or light hat. Arm warmers are nice to have, too. You can get by without a cycling specific long sleeve jersey. I'd go with a wool baselayer instead. Just make sure it's a wicking material.

How cold will it ultimately get in your neck of the woods? I wear my knickers down to about 50-55 or so. Below that, I wear tights.