Gas and Oil Home Heating Furnaces - Adding Air Conditioning

Hello all:

I am about to finish 3rd floor, which is attic floor. The AC part I am
not sure how to handle.

On third floor, there is Duct pipe run covered with shining aluminium insulation, my first idea is just cut a hole on the duct
then connector the connector, flex duct, boost, register. Here is
my questions:

1. The duct serves 8 vents already, is it OK if I add two more ?
(although normally only 6 vents open)

2. To connect to boosts, I can cut two holes or cut one hole and
use T-spliter, which is more efficient ? or easy to work

3. Is the duct body has inner sheet metal ? if so how do I cut it ?

4. Whatelse steps or things I need to do ?

Thanks for your help

Your existing air conditioning unit probally will not be large enough to handle adding any more ducts to it unless it was oversized when installes. I would suggest you have a HVAC contractor look at the installation and make recommendations. You will more than likely have to add another unit to supply the attic.