Designing the mixing panel

It's a curse to be an engineer.  I've spent days and days trying to design a mixing panel for my compressor.  First I had to figure out how to set up my bank bottles.  I've sketched it all.

My goal was to be able to run the compressor and either fill a bank or fill a bottle.  Furthermore, I wanted to be able to run the compressor and fill a bank... while filling bottles off a different bank. That is what made it interesting.

Initially, I had come up with doing it using 3-way valves.  It made perfect sense- each bank could either be turned to the bottles or turned to the compressor (manifold).  I could fill two banks at once, and still fill bottles off the third bank.  Here's a sketch of that:  

 But then reality set in.  I can buy needle valves for $12 up to $40 for nice panel-mount ones.  The absolute cheapest ball valve I found was $90.  And $170 for a 3-way panel-mount.  Ouch.  And then, every subject expert I spoke with said the same thing: ball valves aren't what you want.  Besides the up-front cost, they leak, they are expensive to rebuild, and they 'shock' the system when flipping from one side to another.

So we're going to use line valves.  I took a look at Gypsy Divers' setup and liked their big panel.  It made sense walking right up to it.  With that in mind, I came up with this.  Unlike the 3-ways, any gas changing requires two knobs to be twisted, but needle valves also let you do flow control.

At this point, I need to decide on how all these are going to be plumbed.  Flex hose is easy- but it isn't cheap.  Steel tubing seems to be a popular design, so I'm going to look into it further.