CFM = BTUH/(T1-T2)x 1.08 (at sea level). Not sure where the 0.75 multiplier comes from. Are you adjusting for gas fired heat efficiency? If you are using a heating coil you don't need to adjust for efficiency.
Your air changes per hour formula works.
Hopefully you are not getting a 5 degree...
If you want rules of thumb you could start with 400 SF per ton and assume 400 CFM/ton - or one CFM per square foot. No one sets the rules on air temp for heating but your general assumptions are where I would design a system. Anything over 90°F gets uncomfortable and tends to cause temperature...
