My home is new construction; 2 story with a basement. I have a 2 ton HVAC unit. I am finishing the basement and have installed a supply branch with diffuser in the ceiling. That is one 6" branch off of the main supply to a 500 sq ft rec area. I would like to add a second and also a cold air return to the general area. I have 4 questions: 1. Is there any problem installing a 6" supply with a short collar take-off from the bottom of the main supply about 80" off of the floor and about 10ft from the furnace, or would that "steal" too much volume away from the other branches being that it is right off of the main in such a way? The framing and location of pipes, etc are physically prohibitive to come off the top of the main with a take-off as I did the first supply. 2. If this is too much of a "steal" would placing a saddle on a branch going to a main floor supply be functional or again too much of a "steal?" 3. With regard to cold air returns; can I use flexible or 4" metal pipe from my return main to an outside wall and down to a return grill near the floor? 4. If this isn't wise, can I place a 4" pipe or a flexible pipe inside a wall and run it to an area in between the floor joists where there is existing sheet metal serving as a return from the main floor or upper level? This would sort of branch or "Y" into an existing return duct and not directly into the main return.