As others have stated, it depends a great deal on the weather conditions. Of course, I can see that many of us will have our specific preferences. I tend to prefer multiple thin layers in as much as possible, starting with silk, which makes it easy to use a second layer on top, which in my case is a Marino wool blend.
In milder winter weather (up to ~20F), just the silk layer is adequate. I do use two layers of socks, a calf high compression socks and thin pair of woolen socks (my feet tend to get cold). When the temp dips down to about 5F, I have a second layer of fitting underpants made from Marino wool with some synthetic material blend - wish I remembered the name (I always cut off all the tags so they do not scratch, which means I can’t tell you the name of the brand but I’m sure there are many - mine were rated at medium weight). Second layer of socks are made from thicker wool. Between about 5 through -10F, I use a third layer of underpants which is a thick fleece. Even when not windy, I wear a wind-proof layer over the pants, which makes it the 4th layer. My feet have three layers: compression socks, skiing/sports socks that are calf high, and thick woolen socks. If it is a windy day, I may also use wind-proof shoe covers.
I stop bicycling when it hits -10F!

Stay safe and warm.