My last overnight coach ride was about 12 years ago on the Silver Star. I don't think things have changed too much, except you can't use the dining car. You might want to bring some food, even if you're going to play Cafe Car Roulette and eat from the Cafe Car.
Yes, you will need a blanket and something to use as a pillow. I would also recommend eyeshades and maybe earplugs, too, although the coach is usually pretty quiet after lights out. The main advantage you get from springing for business class is access to the diner and a better chance of having two seats to yourself. The actual seat configuration is pretty much the same as coach, though it may be more likely than coach to be a refurbished car. Others who have ridden business class on the Starlight might have more to add.
