That’s a great observation about the sausages tasting better the next day. The same thing happens when I make stew, soup, or chili. It always tastes better the next day. I agree with you that spices give a great flavor and aroma immediately when cooked but have more to offer as they have a chance to sit longer.
In reply to the one question about how long the sausage sits in the fridge…I follow the same procedures as most - from smoker or oven to the ice bath, air dry, then to the fridge for a few hours.
My procedure from here will probably differ from others. After the sausage has sat in the fridge, I vacuum pack the sausage and put it back in the fridge for a few more days to a week before freezing.