You tell me.

If you use a flow hood you will be able to see the amount of cfms coming out of each register. Lets see if you are close to 1400-1600 cfms. Do the right test now that the leakage is fixed. This will also tell you if your existing system can handle the new equipment. What is the static pressure? We want to find out the total amount of air you are moving at a particular static pressure. .05?, 08?, 1.?

You are not done testing. You could have a perfect duct system, but it may only handle half the cfms YOU need.