Check all existing plumbing & repair/replace as needed per code.
Inspect water heater and make sure it is installed up to code (pressure release valve, earthquake straps, and blocking if needed)
Ensure there is a sediment trap installed at the water heater, if there isn’t one, make sure to install one
New angle stops on all water lines.
Check all drain lines & repair/replace as needed.
Check all gas lines & repair/replace as needed.
Make sure the water heater supply line, and hot water “out” line is flexible
Make sure the water heater's pressure relief valve pipe is at least 1.5" and no more than 6" off of the floor.
Install Pro-Flex gas lines at all gas feed equipment (water heater, range, furnace, etc.).
Install water line for refrigerator (regardless of fridge type).
Ensure there is a pressure regulator or install one if there isn't one and make sure the water pressure is between 60-90 PSI.
All other plumbing work described in the Kitchens and Bath tabs