I'm replacing a water heater only I had someone else take it out.

I was looking at this kit that has two flexible metal tubing, two 4" compression (?) metal tubes and teflon tape.

Should I buy the kit or can I just use cpvc for the cold water intake and metal tubing for the hot water outflow.

The old water heater was for mobile home with the cold inlet on the bottom. The replacement heater I bought has both on top.

Either or. Your call. Look at the difficulty in replacing down the road. In both cases support will be needed for the PVC tubing.