Since I spend the bulk of my tent time operating the stove for snow melting and for cooking, I put lots of thought in my cook system.
The entire system is attached to a stove board for safety and handling, makes it a lot easier to light too. The pot size is a balance between weight and ease of preparation. For winter expeditions you’ll want a slightly bigger pot than what’s typically used in summer. This is to accommodate large snow and ice chunks and to allow for more water volume which helps accelerate the melting process.
Think of the water needs you'll have each morning and evening. For example in the morning, two people require water for breakfast, morning drinks, 2 thermos’ and 2 water bottles = 5 liters.
My preferred pot size for a two person winter trip is three liters. This way you can fill two thermos’ and still have a liter of warm water in the pot to help melt the next 3 liters of water. This save gobs of gas and time. For solo expeditions, I opt for a 2.5 liter pot.