possible plumbing issue …

Ok, I’m using 1/2 cpvc pipe to run everything from my water tank, pump, heater, to sinks. Should I have used 3/4 pipe instead ?  I’m getting water, but it’s not coming out fast, it’s coming out but when I turn the hot water on, the heater kicks in and the water slows down, then kicks in real good for a minute then it dries up and sputters and then it runs cold.

Could this be due to the 1/2 pipe ? The temps are there for a quick minute then it sputters out.   HELP HELP HELP