2. The ratings that you are interested in is the CFM ( cubic feet per
minute) at a particular PSI ( pounds per square inch). All the tools
have a minmum rating with the same numbers I.E. 8 CFM at 80 PSI. If the
compressor's CFM is less than the sum of the CFMs of the tools you use
at the SAME time then you will have problems having to wait for the
compressor to fill the tank.

Quite right, Frank, as far as you go. All compressors have a duty cycle.
Air-cooled home shop compressors are often rated at a 50% duty cycle. That
is, they must rest and cool as long as they run. Therefore, for your 8 CFM
example above, you would need to buy a 16 CFM compressor rated at 50% duty
cycle. Dan