That's a very big question that could take several hours worth of work to figure out. If you want to do it yourself, you'll need to get a copy of ACCA Manual D. Some duct sizing information is on the web, but you'll need the fitting loss tables from Manual D to make much headway.Looking for some adivce on what size trunks to run and when to reduce.
Your best bet is probably to hire a mechanical engineer to do the calculations for you. Duct design is not easy.
There's no way to know this without having the load calc data.Do I need additional supply reigsters for the bedrooms?
One for every room except for bathrooms and kitchens.How many returns? ( I was thinking 1 large hallway return)