Hey, that looks like quite a good design in concept. It looks like your not gonna have much flow going through that though. You should be using about a 3/16" thick base plate, and 3/16-1/4" channel area for low restriction, and then a 3/16"-1/4" top for screwing the barbs in. I would highly suggest you invest in a bar of copper, Youll love being able to seal it up nicely. I would just say get a 14" or so bar of 3/16" thick copper and cutting up all your peices for it.
-edit- Also, invest in a center punch
I see those holes are a little off.
Thats my input.
Jon