Ok, current situation, 50 years old oil furnace, and large air
handler 30 years old, and new 5 ton compressor outside for air.
(installed hoping to increase air flow, which it didn't)

Looking at upgrading either to new oil furnace, or just converting and
getting natural gas furnace. Problems now in winter and summer are
there isn't enough air coming out of vents, which I assume is due to
inefficiency or just plain old equipment. With new oil furnace or gas
furnace can I expect more airflow....also keep in mind I need an new
air handler too, does this go with new furnace or is it a seperate
entity?

Any recommendations to a 25 yr old new homeowner?