Couple questions one, if I shut the main water supply to my manifold and shut all single valves that run to everything in the house to add more ports to the manifold, would I need to shut and drain my water heater as well. Second, In order to add the port I need to cut down the hot and cold pipes that go out to the water heater and HVAC unit. The attachments plastic screw on type look like if I cut the pex above them I would still be able to use them just moving them up to were I shortened the pipes.

The red and blue at the top of the manifold is were I plan to cut down and add my ports, those two lines go to the hot water heater as shown in other photo. and the blue line at the bottom of the manifold is from the main water supply I would close that valve.

Hope this helps thanks for replying.