I would put a block off plate on. The diaphgram will get a huge workout if not actually pumping anything. When they go they usually leak gas into the oil, but with no gas it could start pumping oil out. Extra arms and springs flopping around inside an engine for no reason.
For hard line, Stainless hard line is probably as good as it gets. Cu-Ni (Copper Nickle) is apparently highly rated as well but I have never used it. Steel line works, the last roll I got looks like it is copper lined for corrosion. Copper is a bad choice.
For flex hose, a barrier type of hose. I have been running marine fuel hose for low pressure and suction. It is much thicker than the normal cheap parts store hose. I have some in a boat that 10 years later it was still like new. The parts store rubber hose was nearly brittle at the same age. The barrier keeps the fuel away from the rubber. Good thing for todays evil fuels.
Just got some Earl's Vapor Guard EFI hose that I will be using soon for high pressure EFI. Feels very much like the marine hose but has a high pressure rating.
