Yes it definitely needs a belt guard. Some shops take them off when the compressor is placed in an outdoor enclosure.

It may have a start capacitor and a run capacitor. The can (top center) is a thermal protect and maybe a run switch.
The capacitor with the highest capacitance will be the start capacitor...a wild guess maybe 750 microfarads (750 μF).
The run capacitor will be a smaller value....again a wild guess maybe 30 microfarads.
The start capacitor is the one having to work the hardest (phase shifting) and usually fails first.
A replacement capacitor needs to be the same microfarad value.
Also the capacitor voltage needs to be the same or higher voltage.

https://www.amazon.com/Smith-B813-Rotation-2-31-Inch-Compressor/dp/B007ATNHS6

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."