1) Only premium, basic model do not have this function.
2) Nothing wrong if it purely engine sound and not rattling sound
3) Yep. Generally speaking, overdrive OD is the highest gear in the transmission which is 4th gear for basic model. Overdrive allows the engine to operate at a lower RPM for a given road speed, if require power to overtake or uphill, you may opt to off it but drop in fuel economy.
4) Nope. You may wanna check is the air-con vent air flow direct to the window first.