1. Yes
2. Probably not enough to notice.
3. Your vintage of 6.0 engine has 300hp and 360 torque. The newer gen 6.0 has 360hp and 380 torque. Also, the 6 speed transmission that has been mated to the 6.0 liter since 2007 is a vast improvement over your 4 speed. Also, the newer trucks have a stronger frame, larger brakes, and class V receiver.
4. If the 6.2 ends up in the HD trucks, it will be better but at this point that is purely speculation.
5. Yes, the longer the trailer the more likely sway will be a concern.