Yes on the copper line work hardening.... to help relieve that if you use copper, then put at least 1 loop of copper line between the engine and the body to absorb the movement without severely working the line.
With a braided line, you might want to 'crack' the fitting at the gauge a tiny, tiny bit and bleed a braided line to get the trapped air out and make the OP gauge more responsive; its ID is considerably large than a plastic or copper line, and will trap a lot more air and may make it slow at start-up. But don't make a mess!