I was were you are when I started my years long re-think of what an Airstream could be: I knew next to nothing about plumbing, especially RV pluming.
Faceless friends here on the Forum taught me how to build a very good system.
You can follow the whole coaching process here. See post # 55 for photos of the plumbing system completed:
GNORTS’ diagram will be very helpful. I’m not sure if he is indicating a by-pass at the hot water tank or a slick way to fill your holding tank from the inside, instead of from outside, like Journalist did.
You should have a hot water heater bypass ( that way you don’t have to waste 6 gallons of antifreeze every time you winterize), an inside fill for your holding tank PLUS a valve set up that allows you to use the water pump to winterize your water lines.
I have all three advantages. ‘Hope the information here helps you.