Dry cold is much easier to accomodate than wet cold.
I only wear gortex when it is raining. It is simply not breathable enough compared to a windproof shell. A windproof will keep the cold air from chilling you, but will allow all the moisture through. You wont need to use underarm vents which let the cold air right to your skin.
I have a "huff test" for cycling windproofs. Hold the material against your mouth and give a strong huff. If the wind goes straight through, its not windproof. If you can't get any air through (like with gortex) its not breathable. If the air travels through slowly at high pressure, then it will do.
I have used a dense weave polyester cotton smock, pertex, and polyester microfibre, all with good results, and all about 1/3 the price of a gortex.
For inner layesr, you dont need cycling-specific jerseys, that rear pocket is worse than useless under a windshell. I find that a cheap wickable hiking jersey is good. For mid-layer insulation, thin woolen sweaters work as well as any fleece.
Some cycling leggings have a built-in padded liner. Dont get these, you have to wash them after every use. Use unpadded tights over shorts.
You may need a larger size shoes, to take 2 pairs of woolen socks. Mesh shoes let in all the cold air. For a 6 mile ride, its probably to much hassle using neoprene overbooties, just get some sensible lightweight hiking boots/shoes.