I find I can work in most weathers,.. below 0c you have to pick & choose your jobs (eg not splash water all over a busy street etc) and below -5 it gets really challenging even with a hot system.
I always spread salt BEFORE I start, and I use a lot of it, about 3 kg on a 3 bed semi. If you spread it before you start then the water passing it, flowing over it will pick up salt as it goes & all the water will be salty. If you spread salt afterwards, you only melt the patches the salt directly touches & its hard to get an even coverage I find. Below -6 salt simply does not work though,.. you need proper "Ice melt" type products.
I always prevent my van from freezing overnight. In the morning I run my heater for 5 mins before I leave the house, just to circulate warm water through the hose reel,.. that way when the hose touches the ground it won't immediately freeze. When its really cold, I also fill my trad bucket with hot pure water before I leave the house, as frozen brushes/jets can be melted in seconds just by dipping them in the bucket.
My biggest problem in the cold weather is driving to work. The roads by me are rarely salted, and its not worth risking my life when the roads are impassable.