1. A = pi*r^2 = 3.14159in^2, P=FS*(F/A)=1.3(120/3.14159)=49.7psi. Note, if the cylinder were retracting we would need to subtract the rod area from the piston area. Note: this air pressure is much higher than normally found in a shop, so it would not be practical, and a redesign would be needed.
4. 3-phase power is ideal for large loads such as motors. Single phase power is suited to small loads, and the power usage on each phase must be balanced someplace on the electrical grid.