I have been measuring air flow in houses for 17 years using accurate,
expensive instruments. 1/2 of the houses I measure have 1/2 or less of
the required air flow, so efficiency is already poor. Cutting air flow
without measuring what you already have is a bad idea. You could ruin
both your furnace and ac. Zoning systems require complicated and
expensive controls. They can be effective, but are NOT a DIY project.
More efficient equipment may be a good idea, but it depends on ho
efficient your existing stuff is and how long you will live there.
Sealing ducts that run in unconditioned spaces can help as well.

Stretch