Considering ordering a Model S. Need opinions on options. 1. Premium sound system: is this a must get item? Anybody with comparative experience 2. Smart Suspension: what are the opinions on whether is a order or not. I would be ordering the 19-inch wheels 3. Rear seats: is this worthwhile getting or is it a novel item that has little utility - I have 5 children and probably 3-4 years of use expected based on weight and growth for the back seats. All opinions welcomed.