Power

Compressors produce 4 CFM at 90 psi per horsepower of input [1]
We would want a 12 hour reserve to run all night at 1/4 hp min for various auxiliary loads but not heating. This would be lights and computers, fans, pumps such as for heating.
60 CF storage would be required for 1 hour of such power.
720 cf for 12 hr - or 5000 gallons.

Optimal Specs for Plaster Sprayer

$1200 - Ingersoll Rand, 5.5 hp, 12 CFM @90PSI - [2]
$950 at Harbor Freight, 6.5 hp - 135 PSI - 9 CFM at 90 PSI [3]
$500, gas, 5 hp, 9 CFM at 90 PSI
$600 on clearance, Rigid wheelbarrow at Home Depot, gas, 10.3 CFM at 90 PSI, 5.5 hp,

Let's throw some mud.