A few tips on hard plumbing:
Always use a quick disconnect on each kettle/keggle port.
Design it so it can be taken apart without cutting. i.e. think about how the pipes are attached and use unions if necessary.
Sketch up your stand and keggles and then draw the pipe where you want it. This way you can change it multiple times without leaving the drawing board.
If you are going copper, consider using PEX fittings, they are expensive but far less hassle if you aren't comfortable sweating pipe.
Consider short runs of hose for final connections (braided nylon for high pressure/silicone for high heat).