help with improving HVAC performance on the second floor of an old house
I've been the HVAC industry for more than three decades. To answer both of your questions: The ideal installation would involve installing a return and a supply to each room. This allows you to accurately and more precisely control the climate in each room. The answer to your second question: Yes, you will need to insulate the ducting outside the insulated envelope of your home. If you do not insulate the ducting it will sweat, causing water damage to your home. Home this helps. Hope I answered all of your questions. P.S. Shop around and hire a legitimate HVAC contractor who will size your equipment properly or you might get stuck with the wrong size HVAC unit. Good luck to you and congratulations on your growing family!