THIS is what i plan to build to add on to my existing pond - but probably on a more DIY state
Thanks for everyone's thoughts - saved me from asking a whole lot of questions!
I would ask everyone's opinion on the copper return pipes - i would probably change those out to PVC (you can paint if you want) and at that time you can probably make them larger OD as well. Like someone said - the rule your outflow is 2x your inflow OD, so you dont get overflow.
I would also add that perhaps you can add some different size gravel also - dont have to go just with pea gravel...larger at the bottom with the pea at the top.
To the OP - you're have the making of a good filter - do keep us updated on what you do and how you do it with photos.