120VAC Control Panel Enclosure: Single or Double Pole Breaker for 16AWG Wiring?

I am ready to build my own small control panel enclosure for this home project water heating tank that I am doing.  This will be using 16AWG 120VAC.  I will be using a circuit breaker for electrical protection, but not sure to use a single or double throw circuit breaker.  I know 120VAC only use SPST breakers, Is it the same for my controls panel enclosure that will be using 120VAC power supply?  I've dealt with three phase before, but not really a single phase.   If I would use a sinlge pole breaker what will I do with the neutral wire?  I know ground gets mounted to the frame and the black wire (hot) goes to the input side (power infeed) of the breaker.  I know double throw breaker has two hot wires (240VAC).  Do I use a double pole breaker for 120VAC and use both the black and white wires?  White wire will be wired in one pole and the black wire in the other pole then ground to the frame?  Am I totally wrong?  I will be using terminal blocks that will contain jumpers, electomechanical contactor, heating element, and a temperature controller.  All components will be 120VAC.  If you have any questions for me please feel free to ask.  Thank you very much.

 

Look up the electricity regulations for your country (or state).
Theses will tell you how to wire a system up.
In New Zealand, in a single phase system(230V), you are only allowed a breaker in the phase circuit. All the neutrals go onto a bus bar, grounds onto a separate bus bar, and a link is placed between the neutral and grounds.
Cheers,
Richard

I'm in the United Stages.

That's why I said look up your own wiring regulations. You need to get it right, you could negate things like insurance in the event of a fire, for example,
cheers,
Richard